I have like 2 minutes of experience with the revalver demo, and zero 6505/5150 preamp w/ impulses experience, so I don't really know the subtle differences that would be apparent in each, so I don't feel qualified to make an informed guess.
I'm hoping though, that A is the real amp, because B sounds muddy and a little poopy to me, and considering the fact that I'm getting ready to spend quite a bit of dough on a 5150, I'd hate to think that I prefer the revalver clip.
I'll just throw an uneducated guess out and say A is the real amp, for the mere fact that I hope it is so. Part of me kind of thinks I could be wrong, though, as Revalver is made to sound good with impulses, while the 6505 doesn't even know what an impulse is, so that might give revalver an edge clarity wise.
Oh, and correct me if I'm wrong, but wouldn't the real amp clip be missing a power amp stage simulation? Unless of course a power amp stage is part of the impulse file, but that would mean (I'm guessing) that Revalver would be modeling the poweramp stage twice, which may or may not have much of an audible impact. If I'm right on either of these notions, though, I would say if there is an audible difference from either the presence of power amp simulation or double power amp simulation, it would be in the form of added "softness" which may be percieved as mud, and the "power ampless" or "single power amp" clip would seem to sound a bit clearer and tighter in my imagination. A! Fuck I don't know.