I'm running T5HO's for both Veg and flower right now, so I guess I can comment on this. 6500K for Veg and 2700 for Flower. I run a 6 bulb 4' T5HO fixture with (2) 6500's
and (4) 2700 bulbs and my buds are tight. I use a 2' T5HO as a supplemental sidelight and have LST'd my plants.
Lights are 4-6"s above the plants with a fan blowing down the gap. The T5's DO throw some heat, especially if they don't have a glass face. Good results with them, though I have a 150HPS I will do a direct comparison with when I drop 2 more into flower tomorrow.
2 under 35,000 Lumen's (about 500 watt's) of T5HO, and 2 under 150 watt HPS. These are short bushy plants so I am able to get away with 2 under the 150HPS...should be interesting anyway.