There are forums that cater to the M1/M14/M1A. They seem to be hidden in the mix. Here is one I frequent: http://www.milsurps.com/forumdisplay.php?f=108
Now to your question.
M1s and M14/M1As (as well as any other autoloader) have a preferred burn rate (that is most likely not the proper term). Anyway, if the burn is too fast, there is high peak pressures and low velocities. If the burn is too slow, the chamber pressures are still high as the action is trying to extract the caseing.
As with every other weapon, heaver bullets shoot slower and go farther. Heavy bullets, loaded on the warm side are not good for the operating rod of a Garand. There is variable gas plugs for the Garand, I have one for just in-case use. The M1A is very forgiving and a very, very strong action. But I don't see any reason to be brutal to the weapon or brass, I load nice.
Powder selection is well served if in the range of say IMR 3031 to one of the 4895s. Faster and slower powder work, but worry with heavy/light weight bullets later on. I use 748 exclusively in my M1A (and M1s) and have no problems of any type. I have read that 748 is temperature sensitive, I have not found any indication of it.
With my weapon, loading process and components, my standard loading for my M1A is 43.0 grains of 748 for 2677FPS with a 150 grain FMJ. My loading of 47.0 grains only pushed the velocity to 2762FPS. I save the 4 grains of powder. I know I can push 150 grains slugs faster. (46.0 grains of H4895 will push 110 grain VMax at 3103FPS).
My loads are safe in my weapons with my components, loaded my way. This doesn't mean that they are safe in other weapons with other components.
All way error on the side of safety,