I've been enjoying nearly flawless performance from the Catalyst 12.6 driver set for my Radeon HD 5670 on Windows 7 x64, but as I always need to test new driver releases for my own products, I'm about to download Catalyst 12.8, released on August 15th, and see how it works with Photoshop CS6 et. al.
The drivers are here (for Windows 7 x64): http://support.amd.com/us/gpudownload/windows/Pages/radeonaiw_vista64. aspx
The release notes are here: http://support.amd.com/us/kbarticles/Pages/AMDCatalystSoftwareSuiteVer sion128ReleaseNotes.aspx
I'll report back when I've got the drivers in and have done some initial tests.
I invite and encourage you to post your experiences with Catalyst 12.8 here as well.
-Noel