T5 is low heat low power but high output. I'm on 4 th week flower now using t5 for veg then I swapped 4 of my 8 bulbs for 3000k.
This is a little bit of a misconception.
A 400W t5 panel will output as much heat roughly as a good quality 400W HPS. With input to light conversions of, the rest being heat loss, 10-15.63% efficiency for t5s and 12-22% for HPS there's 12-22% efficiency for roughly 20-33% less heat from t5. However, a 400W t5 will tend to use more like 435-440 watts of actual electricity where-as a HPS uses about the same as long as it's a digital ballast.
Both waste the extra as heat automatically. However, most HPS lights have ballasts separate from the light and thus that extra 35-40 watts of heat can be avoided unlike most t5s. Also the heat from a tubed HPS can more efficiently be vented out of a room, thus saving on overall room cooling if only by a tiny percentage.
I tried both and with my tent setup I had heat troubles from 2 400W 8 bulb panels but never from 2 600W HPS. I also couldn't get as good of light penetration so while I could get decent yields it required a TON more canopy management using them for flowering.
In the end I would totally go with HPS any day of the week over t5s for veg and flower but that's just me. Eventually I'll get some LEDs.