The XXX has plenty of gain. I would say it has almost as much as the 5150II(I've had both). I always thought the 5150s got a little to noisy when you take the gain past 5. The XXX seemed pretty quiet. Maybe because it has 3 less preamp tubes. Both are great amps though.
Also, the XXX has the adjustable levels on the effects loop the 5150II does not. But the 5150s has the resonance control knob on the front which is cool too and the XXX has the 3 way resonance switch on the back.
Tough choice.
