Also consider the fact that they don't need a lot of power to get loud, so don't get hung up on how much you can throw at them.
Without knowing more about the guy blowing them on 750watts I'd take his experience with a grain of salt. Could have been clipped to hell, bass boost all the way up, playing way below box tuning, etc...
I've built 2 sets ups with 2 15" SDC's: 1 off an AQ 1200D the other off a kicker 1500 and they both were tuned to 38Hz and slammed on the lows and sounded very good.
Got another build coming up soon with 8 15's off a couple of Sundown 3ks, so 750watts per sub. Plan to tune this one to 35Hz for a low end monster. Shooting for 150+ around 30Hz....