The Tweaker is great, but looking at the wattages of Jim's existing amps, I'd point him toward the Rebel 30 2x12 (much more versatile than the Reb 20 or Tweaker) or even the Renegade 18/65 watt 2x12 combo (they have several other combo's).

That said, The Express 5:50 and the Alchemist are both incredible amps, and are easily among the best I've ever played. You can't go wrong with either, but the only issue you might have with the Mesa is the lack of a super jazz clean. That was the only short coming I could find.