T5 fixture/bulb question

Hey everyone!
About four years ago I bought a 192 watt, 24", 8-bulb, T5 fixture, and I am almost positive it uses non-ho (high output) bulbs...
I haven't bought bulbs for a couple years, but I can't find any 24 watt, non-ho bulbs, but I can find regular 13 watt bulbs...
Would you rather:
Use the under-powered, but correct bulb for the fixture?
Use the correct wattage, but high-output bulb?
I'm thinking the lower watt option would allow me to never change the fixture, but the HO bulbs would drive it to death fairly soon??? I have done searching, but I couldn't find anything too specific...
Thank you!

Guess I'll complete this circle...
I started thinking that I couldn't find, and/or, they don't make 24W, non-ho bulbs that are the 22.25" (tip to tip) length, so I took the fixture apart and it is a high output fixture...

24w is high output 13w is low output and both the same length 22.5" or whatever. Use what the ballast is rated for so ho for ho ballasts or 24w bulbs not 13w. Its rated for ho anyway and 13w is not bright compared to 24w in the same length.