Cartridge loading question

Does lowering cart loading impedance only affect the top end (rolling off) or does it also impact soundstage, dynamics, etc.?
Moving coil, moving magnet, or moving iron cartridge?
@bdp24 soundsmith zephyr MKII high output moving iron; thanks.
High output moving iron: The lower the load resistance, the more it will roll off. There is a particular resistance value such that the cartridge will neither ring (overshoot) or be rolled off, this value is known as the 'critical damping' value.

If at critical damping, the cartridge will not have reduced output in any way.

Please note that when insufficiently loaded (load value too high) the cartridge will 'ring' (distort). The distortion will interact with the human ear/ brain system in such a way as to suggest that it is more dynamic. Don't be fooled by this physiological phenomena.

None of this applies to low output moving coil cartridges- that is a different discussion entirely.
@atmasphere thanks, how will one know when they've reached critical damping by ear without the help of a program or device when having to consider various phenomenas?
You can get pretty close by ear, but to do it you need a stereo potentiometer, wired as a stereo rheostat, loading the cartridge. I usually use a 100K device.

Turn down the control until the highs seem to go away and then back off. There should be no change in volume, just the highs, which should sound normal and extended but not bright.

You will be compensating for other factors in your system but without instrumentation this means works pretty good.
That’s the way Harvey Rosenberg taught me to tune Decca cartridges, also a moving iron (actually, variable reluctance) design; loading resistance and capacitance to critically damp the particular specimen of the cartridge one owned (back then every Decca was different!). I think he called it a tuned circuit. I miss Harvey.
@atmasphere thanks, can you please clarify the following:

"Turn down the control until the highs seem to go away and then back off." What control are you speaking of? I am using a Pass Labs XP-15 if that helps. Thanks.
If you reread my last post, you will see that you have to obtain the control- a stereo potentiometer and then wire it as a stereo rheostat.

Radio Shack used to sell just the thing for about $5.00; this one should do nicely:
@atmasphere got it thanks. I see RadioShack still has them and I still have a RadioShack near me. How do I hook this in to my preamp? A step by step would be great. Thanks again.
You have to find some way to get it across the cartridge terminals.

Our preamps have a load strip on the back so its rather easy. Other preamps may only have settings available from the front panel. If that is the case, you'll have to get some connectors too so that the connection can be made prior to the input of the preamp.

The middle pin and one of the outside leads of the potentiometer are wired together, the same in both channels.  The resulting connections are somehow made to connect one to the + output of the cartridge and the other to the - output such that the pot (now wired as a rheostat) is in parallel with the cartridge.

If any of this seems tricky to you, you're going to need some assistance when you set this up.
Thanks @atmasphere, really appreciate the help. I will look into this further. In the meantime, I'm really liking what I'm hearing at 250 ohm.
All good advice above.  Sounds like 250 Ohm is ideal for your set up.  Enjoy.
@stevecham thanks, highs and lows both sound good at 250 ohms. I think the lower value plays to my listening room (hardwood floors, lots of hard surfaces, etc.)
@asp307 , as with most MM/MI cartridges the Zephyr is specified for loading at 47K or higher.  I'm surprised it sounds good at 250R.
^^ That does seem like a low value for a moving magnet- I would have expected it to be 10 to 100 times higher!
@dgarretson @atmasphere thanks for your feedback. I am trying different loads to see if I can hear pros and cons and I can. Currently I am listening at 1K ohm. It sounds great however there is a bit of distortion. Possibly it's the recording, I am not certain and it certainly isn't present all the time. More extension of higher frequencies than a lower load. At 1K the speakers seem to disappear.

47K ohm to my ears sounds a bit thin. All the while I have upgraded outlets, power cables and a clarity cap/juniper bypass at varying levels of break-in. 
Sounds like something is amiss with all this. Let the cartridge breathe at 47k.
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47k or 100K sounds best but it depends on your cartridge
100K is an extremely high loading. I don't know if any phono cartridge manufacturer who suggests such a load.
Mistake 47Ohms and 100 Ohms  sorry my Transfiguration Proteus is loaded at 100 Ohms sorry dude!!