2x150w should be plenty, but its best to use 10k bulbs with actinic supplementing. If you used 14k bulbs (and esp. 20K), the sacrifice in PAR may be too much.
I have 2x150w MH on a 65. Sure my SPS are in the top half, but Ive not seen many people that put them in the bottom half anyway. Thats for LPS and softies (zoos, etc.)
I even have 2 clams in the sand bed that are doing well.