Mobile Bay Reef Keepers

Sup gang, I am looking to scrap my canopy and go open top on my 120g (48x24x24). I've been looking at a few different pendant fixtures. I was planning to go with 2x250w hqi pendants. Problems is, all the fixtures I like are pushing $800-$900. So I started looking at some t5 setups.

http://www.reefgeek.com/lighting/T5_Flu ... ght_Supply

This is what I am seriously considering. I also am taking into consideration:

Operating costs,

Bulb replacement cost,

Penetration,

Heat!

Based on wattage the t5 should be more efficient. At about $21x6 or $65x2, not much difference per change but what about duration? I've heard from 6mos to 18mos on both, any opinions or good reading on this?
I think the heat issue give the t5 another advantage if wattage=heat output.

My main concern would be lighting a 24" deep tank. I'm coral-less from Katrina still but would like to get back into it.

If they are normally driven, you are looking at at least 18 mos. There is the very real possibility of getting more. If at all possible, I would recommend an 8 bulb fixture for a tank of your width. You may even wish to go with a retrofit kit--plenty for 24" depth. It will give you even more intensity, being even brighter at the bottom of your tank than a halide fixture. I use a 6 bulb retrofit (overdriven with IceCap) on my 75. I may even upgrade to 8 in the future, though that is likely overkill for me . Either way, the 6 bulb fixture would still work pretty well, just not as much coverage. Oh, and it would also benefit you to fan cool the fixture, since it can increase intensity by as much as 20%. I wholeheartedly recommend T5 lighting and I don't think you will be disappointed.

for the extra 60 dollars, i'd go with the 8 bulb t5 fixture, instead of the 6.

http://www.reefgeek.com/lighting/T5_Flu ... ght_Supply

there is a post on reefcentral too, that has a guy who has done extensive research on the T5's and the various bulb configs if you haven't seen it, I'd suggest you check it out.