Is impedence so important for a pick/phono combo?

There are many opinion on this issue and I'd like to have them calrified.
There are sveveral MC cartridges that suggest a load impedence higher than the usual Pre-phono value.
For example the Colibrì XGW suggests a value of 500 Ohm against values fo 200 Ohm (ARC REF) 40 Ohm (Lamm LP2) and so on.
Steelhead and IO seem to handle this value.
Now, is the optimal load value so important in the process of choosing the Cartridge/pre-phono combo?
Yes, it is important. Especially at the higher quality and price levels, where very small sonic details make a difference.

The impedance loading for a cartridge not only affects the sonic flavor of the cartridge, but can also influence the output level and also the internal damping behavior of the cartridge.

It is important to note, however, that not everybody agrees about what is the best sounding load for many cartridges, and it can be somewhat different depending upon your system and tastes.

A phono preamp that allows a wide range of loads to be applied to the cartridge gives you the ability to experiment with loads that might sound best to you. In the absence of multiple load settings, some makers give you the ability to change precision resistors to the value that suits you. You can then buy a range of these resistors, and do the changing yourself.
Allow me to add some comments...first I want to say that I am no tech person but I understand TWL's response (I hope).
I have had an opportunity, this weekend, to listen to the Aesthetix Rhea phono per-amp. This phono amp allows you to set load and gain very easily. I have a Helikon cartridge that is recommended for a load of 100 to 47khtz (??). I had been using my ARC PH3se previous...and it was loaded at 47khtz.

Big difference when I went to the Rhea and set it at 47khtz and then went to 500!!! There it was..body, warmth, foundation.

Alas, the Rhea started to act just shut down for no reason??? I had a call into Musical Surroundings and my dealer...they are also surprised. I am...lovin the Rhea but with some serious doubts. The ARC has functioned for me for 2-3 yrs now with NO problems.

Jim White.....any comments??
Today I'm living up to my moniker Bombaywalla 'cuz I'm writing from Bombay, India! Am visiting the home I grew up in & where my parents still live!

As TWL mentioned above, it is important to get the impedance match betwn cart & phono pre correct otherwise one can severely degrade the sonics of the cart. Electrically speaking, the phono pre impedance should be 10X that of the cart. so that it doesn't load down the voltage coming of the cart. I think that you have this already but, I agree, that not everyone agrees as to what the correct value is over & above the 10:1 general rule-of-thumb as everyone's ears are trained different.
The capacitance in the phono pre + that of the cable & the the internal DC resistance of the cart. forms a low pass filter. Wrong selection of the phono pre input impedance can cause this filter to attenuate freq. in the audio band & give you vastly degraded sound.
There is a good dissertation on this on the Hagerman Technology website or on the AudioAsylum FAQ page (in the vinyl subsection). It clearly states the advantages of selecting the correct impedance. It is shown graphically as well & it worth your time to read it.
Just another voice to say, "Yes, it is important".

We recently tested some very small load changes with our Shelter 901. Most people with this cartridge prefer a load of about 40 ohms (running through a stepup). We tried multiple values between 30 and 50 and had no difficulty hearing the differences between each of them. Load changes as small as 1-2 ohms were audible once we knew what to listen for. You don't have to go to that extent, but you don't want to be wildly off the sweet spot either.

Rwd, LOL from your story of Lyra's "specification" for the Helikon. 100 to 47K?! My guess is they're just pretending to mate well with every phono stage on the planet in order to sell more cartridges. As you heard, the improvement when you load the cartridge properly is significant.
Hey're right! I also checked the Benz M specification I had and it was something similar!!
Have you tried to load the input of your ARC PH3se down to 500ohm? It may give you the same body and warm as the Rhea.
Sidssp, great suggestion. There's certainly no valid way to compare two phono stages without loading the cartridge identically. A couple of resistors should go for a lot less than a Rhea, and resistors practically never shut down intermittently without a reason. ;)
Is there a way to know exactly the optimal load impedence of a cartridge?
Good point Sid...however, I listened to my Helikon through the Rhea @ 47khtz also vs ARC PH3se and the Rhea was simply better at that load as well.
Zender... Yes, there is, but you may not like it.

Listen to your cartridge in your system in your room with your ears, at different loads. Find the load that sounds best. Sorry, but ultimately it's the only way.

The experiences of others and perhaps even the manufacturer's specs can get you close. But there are too many variables for the "perfect" load to be calculated. Every electrical component in the chain from cartridge to speaker coil has an effect, and changing the electrical load on the cartridge changes the physical behavior of the cartridge suspension itself. It's just too complex to model.

This is one reason I chose and love the BentAudio Mu stepups. I can achieve virtually any imaginable load in a matter of seconds by swapping in a new resistor. I can even use pairs of resistors to achieve intermediate loads for which no single resistor is available. Easy, educational and cheap!
Wow! It is that good? I am shopping for a phono amp as well but your bad experience does concern me.

BTW, does the Rhea run hot? I haven't seen one but from the reports I read, there are a lot of IC chips in the box. ICs don't like heat. If it is too hot, they might mulfunction.

Just a guess.

Hi Sid.....The Rhea is quite good and I am disappointed that I cannot hear it at home since this problem has occurred.
I did speak to Jim White at Aesthetix (very nice man) and he told me that the unit that I had borrowed for the dealer is one of the first run units. These units were a bit susceptible to static (even minor static) and this would cause the shut down. He has confirmed that the newer unit do not have this fault and the "fix" had nothing to do with older units that work...are sonically the same.

I hope I can get another unit to test at home..(Sid you are welcomed to come over if I get another). If not..I may order one with the option of the return.