IMHO, 8x 54W T5HO (if they're individually reflected) is WAAAAAY too much for a 75G. My roommate runs 4x54 W over 90G and I run 3x54 on my 55G. I used to run 4x but found that I was losing things like zoos everytime I replaced my bulbs (oversaturation). I have since switched to 3x and everything is groovy.
My roommate's 90G looks incredible (he has a mixed tank, but his SPS that he has in there does very well) under his 4x 54W setup.
This is all assuming though that the bulbs are individually reflected. If not, might as well go with PC.