If you put a lighting fixture into your hood, your hood fans will swirl air around the fixture but won't directly deal with air trapped inside the fixture. A fixture with active cooling built in will give you 30-50% more light output.
You could install fans in the Tek light fixture if you feel like voiding your warranty. Just don't install a 120cfm 50db noise-monster like I did lol
As for overdriven T5's, normal HO T5's are super bright as it is. I was bleaching a lot of my corals even in the lower extremities of my 24" tall tank with my teklight 8 bulb unit (over a 120g 48x24x24).
I'm trying MH next over my new tank to see how I like it compared to the T5 fixture I had before. I like the idea of versatility in MH's. They work for all sorts of lengths and widths in case you're upgrading the tank down the road. And the new advancements in reflectors is making MH's just as new and exciting as T5's new bulbs (fiji pink for instance).
And "picking the right such-and-such technology so I don't have to buy it again" never works according to plan
. I've noticed reef equipment is almost like computers and they become obsolete to something else in a short period.
Oh and that ATI fixture's supposed to be the best you can get in north america. Dig around in RC for Grim's thread on the ATI fixture if you like