To me it eats D800 lunch just because of what you said - 400 sounds fat and wide even on the highest notes. Mostly al SS amps sound thin up there. Tube amps are more even throughout the bass register which I find superior for sure. Even representation of notes is important.
I have different equipment at home. For cca. 5 years I've been exclusively gigging with my ex SWR Goliath Sr. 610 as it was the only cab I owned at the time. At that time I was doing cca. 100-150 gigs/year. Did it no problem.
I also have a Fame 300 tube, and an Ampeg SVT-CL + Fender Bassman 135 on loan (for 2nd year now). I take an Ampeg or Bassman on basically every bigger gig I get. Every chance I have to justify taking such a big amp with me I do. Because it sounds better, smoother, creamier, wider, fatter, richer, more even etc etc.
My Ampeg SVT3Pro is really the only non power tube amp that I ever tried that sounds close to the SVT-CL which is the sound I admire much. In reality, it is the amp that I go to when I play smaller gigs. Never played a small amp that sounds even remotely as refined - str900, reidmars, gk mbs, vanderkley aurora, glocks (heart and blue soul), Trace elf, Tonehammer 350 and 500, Ag500DC, D800, etc etc (the list goes much longer). I also have a GK1001-II which is famed for its tube emulation circuit (or so called G.I.V.E.) to optimise the harmonic content, but having 3 tube amps sitting in my rehearsal space I can safely say that it doesn't really sound like tubes at all. Allthough it sounds cool, definitely a step above usual SS amps.
Edit: To add, the Str900 came pretty close to the note thickness in the upper register, it sang pretty nicely. But it somehow lacked the balls my other tubes have. It was a very decent downsize though. But as I said, I am a person who doesn't want to settle on compromises.