At the moment, I'm using T5's in my cabinets for veg and flower. I was using hps, but I prefer the more even heat distribution of the T5s. I was able to get the fixture closer to the plants and make the cabinets shorter, Since I grow in my furniture, it made it look a little more natural. Make no mistake tho, T5s do produce a good amount of heat. maybe not quite as much as hps of same wattage, but pretty close. It's just not coming out of a single point.
And regarding power, 400w is 400w. The T5s are about as efficient as hps. Not going to save any money there.
And if you truly want to get yield like a hps, those reflectors are a must. expensive, but your plants will get 250% more light than a flat polished reflector.
Not trying to discourage you, as said, I use them myself. Just giving as much info as I can.