I don't recommend running at 0.5 ohm, but that's just me personally. It's puts too much stress on your equipment, makes a lot more heat, and you've definitely gotta have the electrical for it. With that said, I've run my VFL120.1 at 0.67 ohm with no issues, but I like to keep it above 1 ohm. I'd go with the sq2200.1, soundstream Rubicon 2500, vfl4480 or similar if you can swing the extra cash, no sense in buying a 1200w amp just to save up and buy a bigger one. I have a lot of experience with both subs, and I'd take the xfl over the hds3 any day. I've had good results running the xfl's at 4.75-5cuft net tuned to 32-33 with 18-19 sqin. Per cube of Port area.
Sent from my G870a on 38's.