Contemplating a switch to T5's

[impreza]

The T5 will be for my 28G JBJ nano-cube. I have a few SPS and a few clam's, but don't plan to do an SPS dominated tank. I am more so wanting a clam, acan, zoa, type of tank. Would 6 bulbs be overkill for my purposes? Or should I stick with 4 bulbs?

Also, what are the major differences between the Sunpower and the Powermodule? Is the Powermodule worth the price difference?

Thanks,