I'm a huge 700rb-II fan, myself - but there's no denying that both are great heads...
Even though I mostly gig thru an M-pulse 600 these days, I still kept, and am definitely keeping one of those fine amps... I recently bought a used BL600 on the cheap, just to leave at my rehearsal space, and it's pretty good, too - 'lotta bang for the buck when you go G-K!!!
- georgestrings