The '76 is mine. It's a nasty mofo. The 6550's give it a barky punchy sound. I also have the '71 with EL34's, which is smoother and more compressed and saturated. Which in my opinion is better for 80's style rock; RATT, Dokken, VH, Ozzy, Sykes etc... The '76 can be fine for those sounds but seems most comfortable with spanky rhythms and leads; AC/DC, JET, The Who, The Cult, Joe Walsh etc...
Anyway, that's just one man's opinion. Dave is the master of Marshalls. The '76 is a JMP MKII with all 3 mods, no addtional deep switches or anything and sounds like heaven and hell when you stand in front of it.