ok...
T5's need to be HO driven with a reflector for each bulb to make them worth while.
A T5 setup where you have 4 bulbs for every foot of tank (front to back) is VERY close to a setup where you have a 250W MH light for every 2'x2' area and much better than PC lighting.
For your tank, T5's would be a very economical choice because your tank is only 1 foot from front to back, thus requiring only 4 T5 bulbs. You'll have the fun task of sourcing out 7 foot T5 bulbs though haha. This would only draw 150W. MH lighting with a similar, or slightly higher output, would require 3 250W bulbs for a similar output.
Here's about bulb life:
MH bulbs don't last forever. HQI driven bulbs can sometimes last only 9 months because the bulbs are overdriven. magnetic (standard) ballasts or electronic ballasts allow the bulbs to last for 12 months. Remember, most of the reef tank MH bulbs emit is blue, and our eyes are most sensitive to red; our eyes can't notice the drastic drop in performance when a bulb reaches 12 months because we can't see the blue spectrum that well.
T5 bulbs when overdriven, or if you're keeping high demand SPS at 18" in the water or lower will require the T5 bulbs to be changed every 6 months. Otherwise you get 9 months out of them.
Now consider the bulb costs. 9 months for $200-250 in T5 bulbs. 9-12 months for $180-380 in MH bulbs (depending on brand you choose. economical XM or pricey geisseman). They can work out PRETTY close if you're using economical MH bulbs. Oh, IF you can get 7' T5 bulbs and a fixture/retro kit for them, it'll be VERY economical, since the price difference between 2, 3, 4 and 6 foot bulbs is very small.
Now for power costs. In your tank, T5's would benefit. Lighting the surface area of your tank would only require 150W of T5 lighting, while MH lighting would be around 750W! (3x250W, and even MORE if you're using HQI lighting). So if you were to compare the cost of replacing T5 bulbs to replacing economical (yet still quite good) XM metal halide bulbs, the power savings would make T5's the same in cost, if not better.
Also, the 150W power requirement makes a lighter load on your breaker, virtually eliminating the chance of having to beef up the power rail supplying your fish tank. It would suck to have to reset the breaker every time somone's vacuuming.
as for temperature, I think they're both the same. If the ambient (room) temperature isn't higher than what you'll be running the tank, a good fan or two can deal with any temperature problems. If you can find one, those 6" clip on fans work well. I couldn't find one, so I'm using a 110cfm (very high output) fan from radioscrap that's AC powered (no transformer needed).
What I was talking about, is there's a thread on reefcentral.com where Grim Reefer is reviewing an ATI branded T5 fixture which is JUST arriving to north america. It has INSANE light outputs because of it's superior reflectors, and it's properly cooled bulbs. The sunlight supply fixture uses 'passive" (or 'no') cooling.
The sunlight supply fixture had an output 160 or something (close to 250W mh lighting).
the ATI fixture had like 330!
somone put 3 computer fans on the top of their sunlight supply fixture, and it increased it's output to 250, making it much more intense than 250W lighting (the mod I'm going to try this weekend. I'm just slightly nervous because it'll void my warranty).
If you decide on T5's though, you'll probably have to retrofit them because of your tank length, and that means you get better control of your cooling.
hope that helped. You can swing in to Gold's aquariums when Albert's in. He knows a ton of info, and I usually turn to him for advice, and he can tell you what can and can't be ordered in Canada.
here are some links to reflectors and ballasts n stuff:
http://www.sunlightsupply.com/produc...s%3D%26pgi%3D3
http://www.sunlightsupply.com/produc...s%3D%26pgi%3D3
http://www.sunlightsupply.com/produc...s%3D%26pgi%3D3
http://www.sunlightsupply.com/produc...s%3D%26pgi%3D1
look at the price difference between the 5' and the 2' bulbs, above. that's why T5's can be economical on your system