Re: Mesa Mark III or IV?
I have both Mark IIIs and a Mark IV--but--I don't play the type of music you're into. Makes it hard for me to make a recommendation. I do play a lot of different types of pop music, from Blues and Classic Rock, to Jazz and some Classic Country. I try to emulate Clapton when I play my G&L Legacy, and I like the smooth, singing sustain of Santana. The Boogies get me those tones. The Rectifiers are in a different league altogether.
I played in a band in the '90s with a guy who had a 5150 for a while. I always preferred the tone of my Mesa Mark III half-stack. Every guitar I used sounds good through this amp. I"m sure the 5150 has more gain than the Mark III, and probably a tighter bottom end. Likewise, I'm also not that keen on the XXX. I just don't need that much gain from my amp these days. If I did, I'd probably have to get a Marshall, or at least a Metal Zone! LOL!
The amp that Peavey makes that continues to impress me is the JSX--the Satriani signature. The Cleans are very good, the Crunch is very good, the Ultra Gain is pretty good. I don't think it sounds like a Marshall, nor does it sound (chug) like the Recto I compared it to. I don't think it has that Mesa Mark Series singing lead voice--to my ear, it didn't sound as smooth. Were I forced to choose between a Recto, a XXX, a 5150, or the JSX--the JSX might get the nod.
Oh, and one of the most absolutely hellaciously loud amps I have ever heard--Jake E. Lee at a club in Seattle about 10-12 years ago used two 5150 stacks-dimed. Holy C%@P!!!! At that was on the NORMAL channel, LOL!
The best advice I can give: If you can try the amps under the circumstances you will be using it--that's always the best way to judge.
Bill