A new beta set of Catalyst drivers was spotted at one of the vendors. This is revision 9.10 beta (build 8.660 RC7) and come with full Cypress (Radeon 5800 series) support.
The drivers have been repackaged and have the 32- and 64-bit distributions emdedded in them.
We have a discussion thread open on these drivers right here.
Have you read out Radeon HD 5870 reference review already ?