Cartridge loading

I have a Benz Micro Gullwing low output cartridge and supposedly has a load rating of >400 ohms. I am using an Einstein Turntable's Choice phono section which had 69db of gain and has four sets of interchangeable plugs to vary the load. The problem is, the highest load available is only 300.

When I checked with Einstein they said there is a 500 ohm "load" when using NO plug. They don't make any custom plugs so I am stuck with one of the four sets of plugs that come with the preamp. What does that mean sonically or electrically? What changes could one expect if a 400 or even 1000 ohm load could be applied? Is there an inherent problem with using no plug in the SE slot?

Thanks in advance.
Very close is totally not a problem. What the load does is change the 'tilt' of the output slightly. SO if you want it a little brighter, got for the 500 ohm. If you want it a little less bright toop end go for the 300ohm.
My Audio Research Sp-15 has a selectable impedance switch on the front panel. and I can switch from 30 60 400 800 47K
And switching it changes the 'tilt'/brightness a little

And no problem with no plug in the slot.
Phonostages will show different reactions based on their design. there is no Standard. Phonostage A with 100Ω will sound different compared to Phonstage B with 100Ω (for example). Simply try what is possible with yours and what sounds best, that's it. My choice for Benz is 47kΩ, but not many Phonostages can do that, some sound good, some are thin and analytical. Depends on Design...
Dear Wynnosu : Agree with Syntax post:
++++ " Phonostages will show different reactions based on their design there is no Standard......... try what is possible with yours and what sounds best, that's it. " +++++

Btw, remember that the IC cable has a impedance value too.

regards and enjoy the music,
Your cartridge has internal ohm of 38. Normally 10 times the internal ohm would be the ideal setting. So it is 380 ohm in your case. Definitely try 300 ohm setting. 500 ohm (without plug) could be right depending on your system. I generally load higher to get a bit more top end, but that is my taste.
I agree with Audiolui, A novice or amateur needs some clear
quidance instruction. The 'experts' conditional: 'it depends' from 99+ variables is worthless for the others. One feels like leaved behind in a desert without water. But they, the experts themself, know everything better and need no advice whatever. Exampels: Syntax and Raul.
The so called 'rule' of 10 x internal value is such a quidance instruction. I used 500 Ohm for my Ruby 3 S and use now for the LP S. BTW the designer of (my) Basis Exclusive , Mr. Scheafer gives exactly the same 10 x 'rule' in the user manual.

Oddly, as much as the comments above seem quite varied, I think they are all right. Loading recommendations are just that -- rough guides -- and following them closely does not necessarily result in the best sound. It is possible that something WAY off from the recommendation will be best in a particular set up; to the extent your gear allows for some experimentation, do so, because it cannot do any kind of harm to the gear.

I agree that the particular loading that sounds the best is greatly dependent on the interaction between the particular cartridge and phonostage.

From my own experience, once you get beyond something like 150 ohms, higher values (meaning less loading) have somewhat lesser effect on the sound. For example, the difference between 150 and 300 ohms is FAR less significant than the difference between 50 and 100 ohms. A recommendation of greater than 400 ohms means that the manufacturer is suggesting that very little loading is needed with the cartridge. With most phonostages, the difference between 400 ohms, 1,000 ohms and 47,000 ohms would be pretty slight.

I would NOT worry at all about the difference between the greater than 400 and the 500 ohms of the Einstein. Try the 1,000 ohm as well; I would bet that there would be little difference. If, at 500 ohms, the sound seems a little too sibilant, bright, or lacking in bass, then you may have to experiment with increased loading (a lower value, like 100 ohms). If that is the case, it would be helpful to consult with a dealer or repair shop unless you are willing to learn how to create your own loading plugs or solder in resistors; both are fairly easy to do, but, one would need guidance on the matter.
This has been covered elsewhere but seems to need repetition.

Most Low Output Moving Coil cartridges are unaffected directly by the load, other than the output that have if the load value is too low. But we hear differences at times- so the load is making a difference in some cases.

Here is what is happening:

The cartridge has a small inductance, and the interconnect cable has a small capacitance. Together they form a Radio Frequency (RF) tuned circuit. The action of the cartridge provides the energy to 'excite' the tuned circuit- essentially the phono section is subjected to bursts of RF energy!

Now some phono sections don't care about this, if that is the case you will find the stock 47K to work fine. But if you find that the loading makes a difference and is critical, this is because the load value is reducing the 'Q' (Quality) of the RF tuned circuit, thus reducing the RF bursts. IOW the preamp is sensitive to RF!

If a cartridge manufacturer recommends a loading value, it almost always means that the phono section they use has this sensitivity. Further, it is indeed affected by the interconnect cable as Raul pointed out, so the actual loading value is variable. In short I would pay no attention to the recommendation from the manufacturer in this case.

Instead go with your ears. Try it with no loading first. Then try the highest setting offered by the preamp and work your way down. You will find out in short order whether your preamp is sensitive/has a problem with RF.
Atmasphere brought up a reason for having some loading with stages sensitive to RFI. I helped set up a table for someone with a Hovland preamp. We had problems with noise that turned out to be RFI. The factory "default" loading for the Hovland turned out to be 100k (essentially no loading). The unit had to be opened up to find this out and to make a change. Adding some loading cured the RFI problem.

A cartridge manufacturer, I believe Jonathan Carr of Lyra, mentioned another possible reason that loading might help. He noted that the response peak of modern cartridges are so high in frequency that loading should have minimal effect on audible frequency response. However, he speculated that some phonostages or linestages might be incapable of handling the signal level of the ultrasonic peak of cartridges, in which case, some loading might help in taming such peaks.
Oh horror! I use a 'blanco' record (without groove) for the
bias adjustment. Not to determine the bias force but to have any idea where to start. The same apply for the 10 x 'rule' . One needs some orientation 'point(s)' and can 'tune by ear' from there. Or so I thought.
Larryi, Jonathan Carr and I are talking about the same thing.

The 'ultrasonic' frequency can be in the MHz. Sometimes its easier to think of that as RF which is why I put it that way.