JV, I'd think along these lines:
115/210 cab
bass preamp
guitar preamp
power amp
switcher between amp outputs
Play the guitar through the guitar preamp into the 10s through 1 channel
Play bass through the bass pre through both channels into both cabs, or just straight through to the other channel.
I'm thinking 'dedicated' preamps as it's just more simple and authentic. An F2B, Demeter bass preamp, etc., would work for guitar, but you'd miss the stacked gains, clean dirty channel, reverb, etc. you'd see in a guitar fron end.
Conversely, you don't need those facilities for a bass.
Plus it would save a lot of patching: Just leave the guitar plugged into the Marshall pre, for instance. Then your bass plugged into its preamp. Both are already tuned, each preamp is already preset to your tone, etc. Then all you'd need is a way to switch the inputs to the power amp, and the outputs to the cabs.
The Mesa cabs should work fine, albeit the closed back, vented 210 will certainly be bassier than the typical open back guitar rig. But of course you could Q out some of that bottom.
Power ratings vs. amp output: I always lean to more power than the cab's typically posted rating as clean power rarely blows out speakers. It's usually too-small amps pushed way into distortion (the WRONG kind) trying to keep up with the rest of the band. Within reason, though; you certainly wouldn't push a bridged 3000 watt Crest into an elderly 100 watt rating Fender cab.
It'll take some shopping and a lot of listening, but it would be too cool if you make it work.
J o e y
