The fork-aware packfiles are bigger, but not as much as you might think. We give up the "best" delta that git can find, but usually there is another one in the same group that is almost as good.

I didn't have any numbers on hand, so I just repacked our git/git network.git with and without the delta-aware code. A stock repack is about 300MB, and the delta-aware one is 400MB.

That sounds like a lot, but the real alternative is not sharing objects at all, which is more like 350GB.