Well, I'm not saying that T-5's are the best, but I think that some legit benefits would be less heat and probably less energy consumption than metal halides. Just to play the devil's advocate here with the cost estimate above, I think that most people would supplement their metal halides with some form of actinic lighting, whether it be VHO, PC, or T-5 so you have to take that cost into consideration as well (ballast, endcaps, bulbs). VHO and PC bulbs are not cheap to replace and they are usually replaced fairly often (I think every 6 months). T-5 bulbs can last well over a year and many people have seen usable lifespans of up to 2 years which I think is the same for the XM bulbs. Cost to replace 3 XM bulbs - $180, cost to replace actinic bulbs for metal halide combo - $100, total cost over 2 years - $280. Cost to replace 6 T-5 bulbs over 2 years - $150-$200 (depending on how often you replace actinics and how many you have). As for the watts, a 5 ft T-5 is rated at 80 watts, but I believe it is overdriven by an icecap to about 100 watts - so that would be 600 watts of lighting. Correct me if I'm wrong, but is it fair to compare watts when we talk about different forms of lighting? If you compare halides to halides, then watts is a good way to compare how much light two different bulbs will produce. But each type of lighting has it's own efficiency in producing light. I think I read somewhere that T-5's are more efficient at producing light per watt consumed than halides.