I'm currently shooting both. 2 Springfield M1-A's. A SOCOM 16, and a Camp Perry National Match. My .308 AR is a DPMS AP-4 .308 Carbine. To be honest I love all 3. The SOCOM 16 offers a lot of firepower in a small package. The National Match is a bit heavy, and a more specialized target rifle. The DPMS AP-4 is less ammo sensitive than the M1-A models because of it's direct impingement gas system. With the M1-A models you have to use ammo with mid range bullet weights, (150-165 grains). And a powder with a mid range burn rate. Varget and IMR 3031 are both good choices. If you use too slow burning powder you can have problems like bent op rods, etc. The DPMS is much more forgiving when it come to powder and bullet weights. Again, this is because it is not a piston design, and is less sensitive in that area.
I don't know about your M1A's but my owners manual and the one on SAI's web page disagrees with your statement on the ammo type to use.
I will state that I do load my .308 for my M1A with the same type of powder and bullet weight as I do for my .30-06 for my Garands. As for the SAI owners manual recommendation -
The M1A is designed and built to specifications to shoot standard factory .308 made to SAAMI specifications or 7.62x51 NATO ammunition. The specifications for standard
military ammunition include harder primers to withstand the slight indentation from the firing pin when the bolt chambers a cartridge. This slight indentation is normal.