@swimmerm, my 2nd comment offers some solutions for you and other users coming here with the same problem with their PATH. It should be done on user side. I don't offer to implement this in Gpg4Win installer.

On the issue, I think there are several possible solutions, better than current:

1. Warn user that PATH is too big and tell him which dirs should be added manually
2. Warn user that PATH is too big but still modify it. He has to modify it with something else than UI, so it's for expert users only
3. Ask user to choose between 1 or 2

BTW, there are known solutions to manage with PATH overgrowth.

@swimmerm, look at the files installed in both dirs.
There is no gpg in %ProgramFiles(x86)%\Gpg4win\bin, it is in %ProgramFiles(x86)%\GnuPG\bin.
On the other side, md5sum and pinentry are in the first one.
So, I believe you (and I) should add both dirs to the path.