Looks like it's time for an experiment.
Wire it up, put the lamp where it won't cause any damage if it catches on fire and do a "bake off" test. Let it run for your normal cycle and see how hot it gets. Three things to keep track of:
(1) ballast. Too hot is when the ballast starts to get the fried electrical component smell

If the ballast is hot to the touch, you'll probably want to mount it on the outside of the fixture or to a piece of metal on the surface of the fixture to act as a heat sink.
(2) tubes. these shouldn't get too hot, but it's fun to compare them against other fixtures and ballasts.
(3) fixture itself. If it's a wood fixture box, you don't want it to catch fire.
It helps to have some comparisons to other lamps. I do 2X overdriving of 48 inch T8 bulbs and the Workhorse ballast stays just warm to the touch. I have the smallest APC bright kit and the magnetic ballasts (came with the kit) are too hot to keep your finger on. Some people do 4X overdriving.
This is just my perspective, you mileage may vary.