TT, I had my hands on one of those Peavey Classic 30s for a good while. You're right about the sound. They'll give a Fender a run for its money (but mostly because the specs and circuitry are identical).
I assume you're talking about this little number here?
http://www.carvin.com/cgi-bin/Isearc...P2=VE212&P1=SX
I don't have any experience with that cabinet, but my roommate has the 4x12 (non Legacy) and Mike from my old band also had a Carvin 4x12. I think they sound great. My roommate uses a Legacy head for power. He runs his POD right into the power amp, bypassing all the pre-amp stuff. Legacy heads themselves aren't that great sounding to me (or him), but they're power section is very clean for all tube. I would recommend Carvin cabinets to anyone.
My JBL cabinets are constructed entirely of 3/4" plywood with internal bracing. They are ported on the bottom. And every seam was glued. In order to get to the internals, you have to take the speaker out. They sound really great, but look really bad.

They perform well as a sub cabinet, and as a mid-range cabinet. I love JBLs, but I'd never buy them again.