My 2 cents, T-8 are a smaller diameter lamp. They are electronic ballast I think and are more energy efficient. Probably more expensive than T-12 which is your standard Flour lamp. DR
Dronai is right on about the diameter of the tubes. But it has more to do with it than that. They are more energy efficient, and they will output about the same light. If it is quantity of light that you want, than I would go with a 8’ HO (high output) bi-pins. The energy that you expend will be negligble (T-8’s were developed for energy savings in a larger, more institutional setting. schools, malls, jails, etc…)
The most important thing to look for is the tubes. I would go for a batch of “full spectrum” tubes. They give off a light that is similar, albeit less intense than sunlight. You will find it easier to shape under these, as they show the full colour and will give better illumination. And according to the pshrinks, it is less stressful as well. You might need to order them. I might also buy a few tubes in a “cool” colour. In a blue room they might define the shadows for finish sanding. Hope this helps.