I'm loving the SL for this very thing. I can get the hotter type marshall crunch (800) in various levels of gain on Channel B, but get that nice open Plexi type tone on Channel A. Add a pedal and you can do the almost real clean (depending on pickups) to hard rock Marshall style. SL2 just takes it from there. Two just killer modules.
You can really get that Billy Squire, Foreigner, Early Rush, Seger, Heart, Hendrix, AC/DC etc. type tones on Channel A. I'd also definitely say variations of Page on both Channel A and B.
I'm really glad I picked up the SL.