Okay, here's what I'd do, FWIW of course.
Choose several LPs you're familiar with. This is not a time for unfamiliar music, just concentrate on sonics. Solo piano is excellent. Pick something dynamic that involves the whole keyboard, Beethoven not Debussy or Keith Jarrett. A big orchestral piece with good imaging is useful and natural vocals are too. Don't know if you're into opera or choral but soprano voices are very particular about proper loading. Nobody's as picky as a diva!
I think Benz suggested 47K as the upper limit simply to avoid alienating people with non-adjustable MM phono stages. The optimal load is probably much lower, as others with Benz experience have stated. I'd start right at the bottom of their suggested range, 200 ohms.
Play a selection or two from each LP to get a handle on the sound. At this very low load bass should be fuller, richer, etc. Treble will be less weighty than you're used to. Bass piano strings will sound growly and rich but high notes may lack punch. When I did this I could actually visualize the spot on the keyboard where the rolloff in treble weight began.
Now make a big move up. Don't try to hit the sweet spot by going to 225, go to 400 or even 800. The idea is to bracket the target with your first two tries. Once you establish that 200 is too low and 400 is too high (for example) honing in on the sweet spot is easy. Diddling your way toward it 5 ohms at a time would take forever.
When you get close, tonal differences between loads will become very subtle. The thing to listen for now is imaging. The right load will lend a three dimensional presence and heft to instruments that other loads can't quite match.
