there was a JCM900 SLX 100w in the rehersal studio today. wasn't keen on it at all actually, it was easily pwned by the Orange rockerverb 50 (or whatever its called) beside it, even with the same cab. a little dissapointed.
I think it might be to do with modern Marshall output transformer size?
that could well be, it didn't have any of the guts of our JMPs when cranked. but i also wasn't that keen on the preamp drive, then again, nice 12AX7 might fix that easily.
i tried jcm900 split reverbs a couple of times, but always in isolation, however i believe i might prefer it to the slx. really hard to say for sure though. its very hard to beat a 2204 with a good booster.