I played the same cabs you're currently using about 10-12 years ago, but powered by an SWR SM-900 head. I loved almost everything about the setup, but it was a bit much to haul to the weekly bar gigs. Tonally, I wished I could get a bit more buttery warmth out of it, but I wasn't driving an Alembic back then.
If you can wait until your tour through the US, check out the Schroeder stuff. It will come in extra handy if you do try to gig in the smart car. I have a 2x12 (1212) cab from them and it is great for gigging. If I were more of a slapper, I would probably have gone with the cab that combines a 10 and a 12 (1210). A combo of the 1212 and the 1210 would do everything you could ask in terms of tone and volume. The only down side is that it is too small a stack to look impressive on stage. Each cab is about the size of the Mesa 2x10 and weighs in the vicinity of 50 lbs. I know they were offered in a road ready package as well, but not sure what that does to the weight.
As a side note, I'd say that if you aren't happy with your sound then you need to add more power. Mesa heads sound great, but you don't have the headroom to push the low frequencies very hard in a 300 watt head.
A final thought is that you might try some EQ, maybe an SF-2, to see if that will give you the sound you're currently not hearing.
-Bob