Good info everyone, thx!

I suppose one possibility is to go 12V w/ the RUMBA to start, and if I just end up dissatisfied with heat times, do the 24V upgrade as what likely will be a not too challenging project somewhere down the line. Heck, for that matter, folks are running RAMPS on 24V w/ what seem to be fairly minor modifications but I do like the idea of RUMBA being a little more friendly to it.