Playing with Cartirdge loading on my phono stage

The manufacturers usually know their own products best. I always stick with their recommendation. You will not notice much when you play around.

Which means that you can take some bigs steps.
If they say 50-200 ohms, then you could try 40 or 50 and 1k to bound the problem… If you cannot hear much change from that, then just stay at 200.

Or try 50, 100 and 200 and see if there is much in it.

When you go lower ohms - I hate saying lower load because technically that’s a tougher load for the cartridge - you can start to lose noticeable signal, like 1 dB and more as you slide down below a 10x coil-to-load ratio (about half a dB at a 20x ratio).

This is because of the voltage divider formed between the cartridge coil and load. This only applies to voltage-amplification mode phono stages and SUTs, as intactaudio will point out (though current mode stages are still much less common).

So you may need to adjust the volume slightly on different loads, to be fully fair in your comparisons. You can often notice the difference going from say 50 ohms to 200 ohms (e.g. adjust the volume up almost a dB for 50 ohms load) or vice versa. But at some point, throwing away too much signal (too low of a load resistance) is definitely bad - you’re lowering signal-to-noise ratio for one.

The bottom line is you cannot hurt anything by experimenting with a wide range of different loads and selecting the one you like best. You could even start at 47K ohms and go down from there in logarithmic steps. But it is probably wise not to go lower than the manufacturers lowest recommendation. Ideally, you want to maintain a 1 to 10 ratio between the internal resistance of your cartridge and the load resistance.

I have been surprised that sometimes loading makes virtually no difference and then on some cartridges it makes a small difference. Surprisingly to me I have never gone: “something sounds wrong” and traced it to accidentally changing loading. 
 

You just have to flip through them. 

I recently acquired a Sumiko Starling and between 100 ohms and 200 ohms there is a HUGE difference. With Lyra Kleos, a 100ohms difference is hardly noticeable. Just play with it. Don't listen to anyone about that but your ears.