the t5 is just a high output fluorescent. i think mine was about the same size as berts and i think i was told it was like using a 250w hid but with about half the watts used. the good; evenly covers a larger area with less heat and uses less power. the bad; its not an hid...yield/m2 will not come even close.
heres a site that sells bulbs and has the lumens for each. t5 blows away normal tubes but comes no where near the hid bulbs.
seeing my buddy veg under the t5 is the reason i never really used mine. after a couple weeks of veg his ladies were always skinny and small and needed some time under his 600mh before he put them under his 1000hps. where as the ones i vegged under a 600mh were topped and ready to flip after about 2 weeks. i have no info on the red spectrum tubes or yields in general under the t5.
put it this way, my yield/watt ratio was better when i used 600s but my yield/m2 is better with 1000s. and theres the rub... the more power you use the more you waste. but i only have so much grow area and want to get the most out of it even if i have to use more power and control heat. i like your idea of the 2 400w. sounds like your getting about 1000w of yield with 800w of power. i still need to study up on the nft. my hydro store guys calls it old school method.