what I did and what lots of ex-mils do is take a look at what the people in the competitions are using and copy that as much as possible- there used to be a load for the m14 on the net called the m118slr- 175 grain sierra match king, mag primer and 44 grains of 748 powder-there's volumes of work by ziediker amongst other others- I copied his work religiously,even if it is in 308- you can increase your loads to 06velocieties- mine are a little warmer than his- 180 grains at 2610 vs 175s at 2550- but mine are hunting loads not targets
I was just talking to some of my long range buddies and the reason some of them don't use the 06 length action is that it's "too long and springy" if that makes sense- one of the guys I know that constantly wins matches uses a 308 , the m118slr, and a 10x scope - with a harris bipod- and he's a 1thousand yard shooter- he STARTS off about a yard in elevation-and that's by looking, I didn't actually measure it
and forget factory made cartridges- they're too inconsistent
it all depends on your DEDICATION and your budget-