Yes its overdriven, about 80 watts per bulbs and Four bulbs that 660 can overdrives. 430 is not really overdrive,

SPS will grow under 660 overdrive.

I have 75 gallon too and I am plan to have 4 bulbs drive by 660 and two is also drive by other 660 because I can upgrade to 8 bulbs later when I plan to get other tank.