My wife is only ~250 lbs, though she was around 350 when we met. Honestly, my taste lies in the 350 to 400 lbs range. Strangely, being with skinny girls, I just fuck them. When I'm with big girls though, pound town all the way. Not to mention, most the big girls I've run across love anal.
Beating the fuck out of someone that enjoys it just becomes fun.