Source Fours can be 375, 550, 575, or 750w. 360Q's can be 575 or 750w.
Chris is correct however in that you need a higher power rated dimmer pack if running 750w lamps. Look towards the DP-640B. I have a bunch of them and love them. A lot of little extra features that I use quite a bit and are quite useful (dimming control on the pack, can patch each channel individually, instant on dip switches).