If you have to start somewhere for load data, Master Po's temple has a collection of NRA loading data for the Garand.
I deleted the URL to Master Po's as I have been informed it is infested with malware.
Still, having shot 10's of thousands of rounds through Garands, it is my opinion that with a 150, 47.5 grains IMR 4895 is a max.
Pressure wise, the locking mechanism can take more. Recoil wise, you speed up the operating rod much faster you will experience bent operating rods, excessive peening in the receiver heel, and mal functions. There were lots of malfunctions with the 2001 Garand Match ammunition, that stuff was clocking 2900 fps and the CMP had to tone down the ammunition from all the complaints they had.
If you notice with the data from Master Po, the heavier the bullet the more you have to cut the charge. This is directly related to gas port pressure.
The specification you see about GI ammunition being 2750 fps +- 50 fps is only true in one Frankfort Arsenal pressure barrel. (My guess as to a FA barrel, but it was one barrel) All ammunition acceptance was calibrated to that pressure barrel. That pressure barrel was not a Garand.
The best way to determine the proper velocities for a Garand is to shoot US GI ammo, the earlier the better, when the Garand was pulled from service all that was left was machine guns and I believe the ammunition started getting hotter. You will find that once you chronograph 50's vintage US GI 30-06 the velocities with 150's are about 2600-2650 in a Garand.