I've got 2 HX112s and an HX810. I like the 12's much better but 2 HX112's cant beat the volume of the 810. I've debated dumping the 810 for 2 more HX112's, 4 of those suckers would make for a nice modular rig to cover any size room. Maybe run 3 or 4 HX112s off of a Mesa D-800 (2 ohm stable) would be a good match.
Those Hartke 12's can take a beating. I've gigged them with a LH1000 Bridged into 2 of 'em, just be easy on the bass knob and you're fine. I just picked up a Peavey miniMega (1000 watts RMS into 4 ohms) and it goes great with the Hartke 12's. Havent gigged the peavey head yet but the loud basement test was good.