I prefer a SS amp with my set up (Crest CA9), but use Cygnus into a real cab. My favorite amp is a JMP 2204 and I mostly use the Fractal Brit 800 sim. Both into an '81 1960A.
With Ares, the sound was pretty much right on, but it didn't push as much air (the thump or slam or something wasn't the same). It certainly was good enough though.
Cygnus does seem to have helped make the Fractal closer to the real amp. If I'm honest I might actually prefer the Cygnus Brit 800 to the actual 2204, but that might be because I don't often crank up the 2204.
Cygnus isn't perfect; the 5150 is another amp I really like, and Cygnus still doesn't exactly match the thump and slam of that amp, but it still sounds good enough for rock and roll.
IME, YMMV, etc.