Benchmarking all of these configurations was handled by the Phoronix Test Suite.
In terms of the R500 support, the open-source R500 driver can compete with the legacy Catalyst driver as showed a few days ago on Phoronix. Also worth reiterating is that with the latest upstream Catalyst driver, AMD has removed the HD 2000/3000/4000 series graphics card support so using the open-source driver is basically your only option moving forward. There's also the results of the recent AMD Radeon: Linux vs. Windows comparison.
All benchmarking happened from the Intel Core i7 3770K "Ivy Bridge" system with just changing out the driver configuration / graphics card each time.
If you wish to see these many results on a single page, subscribe to Phoronix Premium for ad-free viewing and to view multi-page articles on a single page. This is a long article with a lot of unique findings!