Not meaning to hijack your thread, but I have a similar, albeit opposite dilemma.

There is a 20" El Mariachi I am looking at buying. This is going to be my first mountain bike, although I've ridden road bikes for a while (usually ride size 56cm). My LBS has a medium El Mariachi but no 20" although my friend has a 20" KM that might make a decent enough comparison to see if the bike will work. FWIW I'm 5'10.5" with a 31" inseam.

Is anyone else around my size riding a 20" frame?