You're the second person to mention using 4064 for the Garand and heavier bullets, actually. I am planning to try out some heavier bullets for sure (thinking 165 or 168 soft points) as I think it would be cool to take a white tail with my Garand this fall. I tried the 150s with 4895 powder first, because I read somewhere that was the closest you could come to the original M1 ball and it was a historic experiment. Now I'm ready to try for accuracy with heavier stuff.
I keep hearing that Varget is good in a Garand too, but I'm a little skeptical since Sierra's loading book says to make sure you always use a medium burning powder and stay under 2700 fps in order to avoid damage to your op rod... which gives more power to your point that bigger bullets work better.
I've heard about Enfield barrels being all over the place for diameter that's for sure. I guess if your barrel is over .312 you really have to make your own, eh? I hear Lee will build you custom bullet moulds for a reasonable price too. My buddy had some made for one of his rifles, and they work good.