Re: Which amp ? Engl, Marshall, Koch or Mesa ?
The Koch is an AMAZING amp, but it probably won't suit your needs for super high gain.
The F-30 isn't going to sound just like a Mark III, Mark IV, or a Mark II+C just because it has the Mesa nameplate.
The Engl Screamer has alot of gain but for the price you could probably find a Engl Powerball or Fireball 50 (or 100)... very high gain, good resell value, and looks to boot.
JVM is a good amp, different than the others but the 410 is super versatile with all the channels,MIDI, and modes etc.
The difference between most 50 and 100watt heads in volume isn't that big, and i'd advise getting one with a hot plate, or built in power cut for bedroom use.
......but with your list it's hard to go wrong.