You need to figure out if the initial cost of investing in a new lighting system will pay itself off in savings from less power consumption and in what period of time.
Since you already have the MH setup, your initial cost would be very low whereas if you were to try T5's, you'd need to buy a ballast (Ice Cap, Triad, or other), standoff, bulbs, reflectors, etc). I'm not saying don't try it (cause it would be cool
), but you have to sit down and calculate it out to see if you are indeed, actually saving money in the long run.
Also, if you keep reading the thread, he swaps out his bulbs every 8 months...so 8 new bulbs every 8 months...adds up pretty quick since those bulbs are about $40CND each...