(I'm not reading all the other pages of posts,)
Here's the tricky part. A 30-06 BLACK-TIP armor piercing bullet might be better than a 62-gr steel-core 5.56 for penetration, but they are difficult to come by these days.
Another thing to consider is why the military dropped the 30 caliber rounds for 5.56 in the first place. You are in the exact same dilemma. Which delivers more effective fire? Your Garand is limited to 8 rounds. It is a VERY heavy, bulky rifle. If it was ME, I could aim a mini faster, fire it faster, and probably deliver more fire on target much faster than I could with a Garand. If you had to reload it, you could reload at about the same speed, but with a much higher capacity than a Garand.
I have had the opportunity to shred a car with a M-4, using 5.56 steel-core ammo. I hosed the same car with an SKS. the 5.56 penetrated everything except the bell housing, engine block, axles, and brake rotors. The 7.62 was less likely to go out the other side. I have an AK and an M-4. I would definitely grab the M-4 with a mag of ss-109 first.