I've used a SM400 for nigh on 20 years and I've swapped out teh pre valve and had it repaird when it fell off stage..otherwise it hasn't missed a beat.
Very well made says the man who repaired it, with top components.
Runs Very hot but sitting in a tight 3U rack inc tuner with no fan doesn't bother it at all.
Extensive tone shaping possibilties.
Stonking amps, IMO/IME and for the price they seem to crop up here for, are a blinding deal.
The best model are SM, IMO, and pre-Fender, U.S made..probably around 1995. These should include a fan and an earth lift as useful features...but I wouldn't swap mine out for one of those, myself as I an entirely happy with what I have.
I beleive the later models also solved the excessive sub feature on the early SM400's as this was a nice idea but not really useful ...if you have an older one as I do..you'll never need to put the bass beyond 12 o'clock..as once you are aware of this sub issue..you avoid using it as it sucks power.
I looked to replace this amp with a shiney new toy...but I can't find one that is as all-round good. Very well made..probably over-specced component-wise, which probably Fender will have down-graded, maybe understandably, massive EQ..but they run great flat on the dial and with enough modern features like an enhancer and limiter..plus true bi-amping capability.
SWR and a jazz is classic.
Top top amp.
Used the Goliath cabs with PAS and they were benchmark as well. Still good today but there are other cabs out there now, IMO.
I never saw the point of premium gear along side a budget line so never used the Workingman series.
I am not sure the x series match up either, so for me it would be SM or nothing at your amazing SH prices
Over here in the U.K SM900's get $600 plus and SM4/500's $500 plus, SH, IIRC. which makes them a LOT of amp for that money.