From what I can gather, these are very similar (and similarly highly regarded) amps. Please correct me if I’m wrong, but as I understand it, both have foot-switchable dual master volumes (for a lead boost in volume only, gain & EQ unchanged), and have mega gain on tap (the only difference being the SL-X uses a 4th preamp tube vs. the Mk III using diodes). Am I correct so far? If not, please advise. I currently own an SL-X head (50 watts). It's perfect for me, with its foot-switchable twin master volumes (for rhythm vs. lead), plus its mega-distortion levels (but note that my needs are modest, as I play classic metal, a la Sabbath/Purple/Rainbow/Ozzy/Dio/Whitesnake levels). However, I’m getting old, and lugging a heavy head plus a big 4x12 cabinet around is becoming an issue for me. A 1x12 combo is starting to appeal to me A LOT as an alternative. These days, with a single speaker in a cab being miked and pumped through the PA — and amp volume kept rather low in most bars & clubs — why not switch to a more easily manageable combo? I wish that there was an SL-X combo model available. But so far as I know, that does not exist. (Again, please correct me if I’m wrong!) So from what I can tell, the next closest thing would be a JCM 900 Mk III, because it has the foot-switchable dual master volumes, plus an extra gain stage (even if diode instead of 12AX7 tube) for more gain w/o need for pedals. Again, would you agree with my assessment? If not, why not? Thoughts? At this point, I’d be open to working out some sort of trade: my SL-X head (50 watts) for a Mk III combo (1x12). Any takers? (Or any opinions as to whether this would be a good or bad idea? I love the features, but at this point — age 62 — would like to downsize).