I mean this to be helpful to the OP's deliberations:
I've owned and gigged extensively an Aggie TH500, a GK MB 800, GK MB fusion 800, and a Mesa D-800. All of those are in the stated budget, used.
The TH500 has a beautiful wooly character. It's baked in the cake, though. It's there at low volumes, and becomes more pronounced the more you crank it. I dig it at low volumes. Cranked, not so much. To my ear, it kinda gets mushy and loses the punch.
The MB 800 is deep and wide on the bottom, with a cutting top end. That's its native voice, and it's hard to dial out, if it's too much for ya.
The MB fusion 800 kinda rounds off the edges on that, but it still has the scoop and the bite. It's my second choice for a loud rock application.
The D-800 is my fave. It can be tight on the bottom and top, when you set the voicing control to min. As you turn the voicing knob up, it opens on the bottom and raises the top. Never quite has the bite the GK heads do. Never gets quite as wooly as the Aggie always does, when you crank the input gain. Has, IMHO, a great midrange character, easy to shape with the EQ.
In terms of cab choices, the Mesa wins, hands down. These days, I run modular. I've got a bunch of single-driver 8 ohm cabs, and I bring what I need to cover the gig. The D-800 can handle four 8 ohm cabs, with no sweat; it was designed to do that.