Ditto this.

If you can drop an entire rack and two packs, you start really getting ahead of the game in weight savings.

What's important to me is being able to ride fully loaded no-handed, and I can do that with my rear-only set-up.

If you get light enough, say under 20 pounds, it doesn't really matter much where you put it. A friend of mine with that kind of load can even ride with it on his back and he uses his carbon frame road bike. He couldn't be happier.