#1
like for example, a website that gives the specs of the different models of marshall jcm 800 amps, or just the general differences between marshall jcm 800's and 900's. i could google the **** out of it, but that'd take forever
#2
Hmm. For all my instrumental needs I always go to Musicians Friend. As far as I know, they don't have side by side comparisons, but you can look at the details of each of them, read reviews, and then compare yourself. Sorry if this isn't much help.