the t5s put out less heat and more light per watt, about 20% more light than the t8s, but you can use the t8 they will just stretch a little more from the incresed light hieght, about 2 inches further away than t5s.
The T5 runs hotter than a T8, this is due to the fact that a T5 runs at 54 watts and the T8 runs at 32 watts per lamp more wattage means more heat.
Most of the fixtures in Hydroponics catalogs tell you that T5 they have 5000 lums per lamp, but what they are not telling you is that is peek lums with a rock solid temp of 95 on the dot to get that number.
I real number is around 4500 lums per T5 lamp and 2500 lums per T8 lamp that is with a HO ballast installed and that's if the light and ballast run at 100% but most T8 or T5 fixtures run around 90% to 93% and they lose 10% over the life of the lamp.
The T8 can sit about a 1" from the top of the plants with out damage if it is a T8 2 lamp fixture, you have to raise the T5 to about 2.5" from the top due to heat, but it is still more light than the T8 due to the higher wattage use.
The T8 total lums for a 2 lamp HO would be 5300 lums and the T5 would be 9300 lums.
The CLF do the same thing for sales on the lums they claim to be 2600 lums on a 42 watt CLF at 95 degrees but they really are only 2200 lums and that would be running 100% efficient. most CFL's are only 88% efficient and they lose 14% of light over there rated life of 10,000 hours.
The T8 lamps have a rated life of 20,000 hours, T5 have a rated life of 15,000 hours, and CFL's are 10,000 hours. Plus a 4ft lamp fixture has a better light foot print than a bunch of CFL's.
So if you were looking to have a nice veg area one 4ft 2 lamp T8 shop light from home depot for around 45.00 bucks, Or you can get a 4 lamp T8 troffer for 68.00 bucks and get around 10,600 lums. It will live 2 time longer and stay brighter than CFL's, plus the T8 lamps are only 4.00 bucks each and the ballast are around 20.00 bucks. You can get T8's in 2700K all the way up to 6500K all on the same ballast.
The T5's are the king of the floros if you have that money to spend.