I would buy the Head at a local shoppe with a reasonable unconditional return policy. Then you can try it out in the real world. I love my Marshall but who knows, Maybe the Mesa would sound better to you or the Orange or even the Ampeg. I think any decent amp can sound great with proper EQ and a competent player. I just love standing in front of my Marshall and hearing the growl but you may want more of an old Sunn/folded horn sound. That sound is amazing. The other bass player in My High school played a Ric thru a Sunn Rig back in the 80's and it was quite thunderous. Certain amps do certain things better but the cab & bass has alot to do with it also. I'm in my Growl phase right now but who knows what the future will bring.

I've been doing just fine with a Traynor YBA200 and either of my Carvin cabs (2X12 or 4X10.) Honestly, it's one of three amps I own and it's my favorite. (I've got a Carvin B1500 that is way too loud for most practical applications and a Gallien Krueger 400RB which is very clean and detailed, but not quite loud enough.) Most of the time, 200 all-tube watts is enough for me, and the Ampegs I've tried (the newer ones) have all sounded like ass...

The traynor YBA is enough for me as well. Anything more would be overkill for my situation. All I'm competing with in my band is a telecaster and a 35watt Vibrolux combo! In fact, I've never cranked it past 9oclock. That being said, I do dream of old SVT's and 2 8x10 cabs (through my Ric) on occasions!