Thank you guys for all the great input ! This is extremely helpful and answered a lot of my questions.. I'll definitely feel better about my decision (once I make it). Who knows... I may not even end up with a GK if I happen to find a different head that I like more. But based on your all's descriptions and other "research" I've done, I'm not even remotely worried that I wouldn't have enough power if I bought the GK 700RB or something else comparable to it.
PS - interesting comments about the effects of different headroom . Actually, one of my tonal goals is more growl/dirt more easily from the amp, so that I don't have to resort to an effects pedal/unit for a dirty sound (since all the ones I've tried are complete tone-suckers)
New Jersey Bassist Club #190