Cartridge Loading

This may not be perfectly on point, but FWIW, I have a Glider medium output and had the ability to adjust impedence on the fly. I went thru values from 47K, way too bright, to 25ohms, way to dark, slow and muddy.

So if you like your system on the lighter brighter and crisper side of neutral go with 600, and for the obverse 200. And if you can't make up you mind go for 400. (FWIW I ended up at 2000 with my Glider).

The problem is that this is a sonic issue not a functional one and unless folks knew what you had and what you liked/wanted an intelligent answer might be hard to come by.

See if you can borrow an ARC Ph 5 or 7 pre. It is a great way to check out the loading since it can be done via the remote control.

I do not want to spend time trying to determine if 400 ohms sound better than 600 ohms

Then you will never know - because nobody else can tell you.

In addition to the factors mentioned by Newbee, the technically optimum loading for any LOMC depends on all the other components in the system, including the room. Anyone who tells you they know a LOMC's ideal impedance only knows it for their setup. Whether the same setting would be ideal in yours is anyone's guess.

If plug-n-play better suits your style, I'd suggest sticking to MM's. You'll save both money and time. LOMC's not only cost more, they take more work if you care about sound (and I assume you do, else you wouldn't have asked).

Sorry if that's not the answer you were hoping for - but IME it's the answer that's true.