Have you guys tried updating to the 9.9 Catalyst drivers? That supposedly adds a Crossfire Profile for ATI Cards in Resident Evil 5 (And no matter what anyone says, all of the x2 cards, despite being a single card, are two GPU units and thus are enabled in Crossfire on a permanent basis).
I'm using a Radeon HD2600Pro 512MB and can run RE5 at about medium-high settings (Max texture detail, medium shadows, medium overall quality, 1024x768 resolution, unlocked framerate, no AA, DX10 mode) and get a consistent 30+FPS, most of the time over 40+FPS with an occasional dip to around 25+ in heavy explosives-filled combat. No lockup problems whatsoever either.
Using catalyst 9.9 drivers too.
Thanks for the heads up on the new ATI drivers. I had just updated to the catalyst 9.8 two days before they released the 9.9. Will see if it makes any difference.