Dang, I still own all these amps.
I've gigged each with the same NV610 cab, and then also with and without my VT-pedal.
My Buster:
No powertube sag, lightning fast attack. Seemed like I'm playing a 500-watt solid state power section to me.(I swear this amp improves my playing speed over my SVT/400+)
Clean-
surprisingly loud lows, bright piercing mids and highs. Punches so hard you'll get bruises
Doesn't seem to poses the low-mid growl tone I prefer, even with a VT pedal into the front-end or poweramp section via F/X-return.
My Buster's tone and feel is as completely different from my SVT-II, as 2 loud tube-amps can possibly be.
SVT-II (non-pro):
Really good punchy-compressed sound/feel with just enough tube sag when played at higher volumes.
Good lows but they get kinda fuzzy at louder volumes. Sweet-musical low mid growl for days, plenty of highs if desired.
Thick rich, syrupy tone that envelops most any room with with a velvety blanket feel, with lots of punch.
I prefer my SVT's playing in my classic rock cover/Americana-original rock bands.
400+:
I truly consider my 400+ to be the halfway point between my Buster and SVT.
With some bands, I prefer my 400+ over any of my other amps.
If I had to bring just 1 amp to a metal band tryout, I'd bring my 400+.