I replaced my ATI 8 x 54W Powermodule with the 48" Vertex Illumina just about a month ago and I am very happy with the results. The Illumina is a real PAR monster, I had to dial it way down (50%W 60%B, 60% RB) to avoid bleaching my corals.
I observe excellent growth on my SPS frags a colonies and the ability to dial in the colours makes this light a perfect replacement for the ATI PM IMO. Also, the fixture is only 12" deep vs. the 26" depth of the ATI so it's much more stealthy over the tank.
A nice bonus is the shimmer that you just won't get with T5's.
Here's my thread on the Vertex Illumina
http://www.canreef.com/vbulletin/showthread.php?t=66180
I'm sure you'll be really happy with it over your tank.
Cheers!
-TDF