Well gang, I saw, I touched, I listened ... to the R500!

And I got a chance to directly compare to an F1 and LMII. (Using my Bergie HT/EX cabs and my Nordy Vj5 bass)
Here's a review I just wrote dedicated to a very fun shootout:
Markbass R500 - F1 - LMII Shootout http://www.talkbass.com/forum/showthread.php?t=356547&goto=newpost
In short, I did
not buy the R500.

Nor did I did trade my (second) LMII for the F1. I concluded that for my needs for an ultimately versatile amp, the LMII is stunning. It is a shining example of what a great amp and a great value should be. It is clearly the most versatile and best sounding amp of the three I tested. (To my ears, IMHO/IME) The LMII has a presence, fullness, and quality of tone couple with awesome responsiveness. It remains incomparable to anything else I've tried. It is especially remarkable at the price point.
Brief synopsis:
R500 - Tube, wooly, spongy tube sounding amp. Reminded me of a DB750 tone. Didn't 'seem' as loud, but that tube slowness might be responsible for that. I may equate the perception of a more powerful amp to the quick, solid state responsiveness of the LMII. I could NOT get a slap tone I liked on this amp. It does not have VPF knob or VLE. (Doesn't need the VLE) It's like the VLE is turned up all the time. Didn't do it for me. But for fingerstyle, blues, old school tone, the R500 might make you happy.
F1 - This is perhaps an over generalization. The F1 sounded perhaps quicker, a little thinner than the LMII. If it sounded brighter, it was because the low's and mids do not have the sweet fullness that the LMII possesses. The F1 however is an amazing marvel of engineering, given its power and performance in a head this size!Day-am. How'd they do that? When played loud however, I felt the lows and fullness sounded compressed. That to me was a deal killer compared to the LMII. But for moderate volumes, it had no excuses to make to anyone.
LMII - The LMII has more presence, and a bit more depth (or warmth if you prefer) compared to the F1. The highs sound slightly richer harmonically. It's hard to describe. The LMII just seemed to present all notes with a sweeter, fulller tone, and punch. When played loud, it was very responsive and just seemed like it had more power in reserve compared to the F1 and the R500. The LMII is simply a great amp. I think I admire and respect it more than ever before. I was able to get an R500-like tone by dialing up more VLE. But I could
not get a good slap/funk tone (in comparison) from the R500 no matter what I tried. If you want to know what an R500 sounds like, dial up the VLE knob on your LMII to 12 o'clock or a little more. Bump the low mids and now you have that chewy tubey tone of the R500.
The LMII is "it" for me. It does it all.
Gary