Local disk rsync

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I've done quite a bit of looking, but I haven't found an answer that
answers this question.

Environment:
cygwin on Windows
rsync 3.0.4

I know that rsync isn't optimzed for speed on local copies - that's
clear in my testing. I'm attemting to sync a large volume of files.

(In this case, I'm syncing a rdiff-backup set...)

An initial sync will be about one fourth as fast a a cp of the same
files. "Ok, that's not a huge deal. Subsequent syncs should be a lot
faster" I though.

No.

Using a native windows sync tool, a sync of the source to the
destination takes perhaps 5 minutes. (~24G, 80K files) However using
rsync takes a very long time. (I've never let it finish, but it's
still running an hour later or more...)

Here's how I run it:
rsync --recursive --delete --verbose --stats --perms --super
/cygdrive/e/somedir/ /cygdrive/f/somedir/

Thoughts?

I'm mainly using rsync 'cause I know it, and use it. If there's some
alternative I'd be glad for a pointer. I don't know of any other good
sync tools like rsync. (Unison I guess...though I only need one way
sync.) [Whole file copy is fine if needed, though some of the files
are large 1 GB+ and a delta copy would speed these up...]

TIA!
-Greg