RE: 7.62 NATO and .308 Winchester- I don't work for NATO or Winchester, so this is my best educated guess- OK?
The NATO round was standardized as a military round, suitable for chambers cut a bit oversized (works even when crud is in the way).
The .308 was standardized as a civilian HUNTING cartridge- not uncommon to find heavier bullets than standard NATO, loaded hotter, brass is thinner (means greater internal capacity for the case)
What difference will you find in the performance? In all likelihood, not enough to notice. However, there are some rifles that BARELY make it to 7.62 NATO strength. I would not want to chance bending my dogtags by running HOT .308 loads thru them. Could you? Sure! At least ONCE.
More than that..... ah, what was that quote from Dirty Harry?
Me, I'll look at the SAAMI website. If they say a cartridge swap is OK, I'll use it. If not, no.