A beta version of the upcoming Catalyst 9.10, signed MSI, can be downloaded from HERE. This version string of this driver is: 8.66-090914a-088589E-MSI (9-14-2009). This driver should support new Radeon HD 5870. There are still 158 (or 159) OpenGL extensions like in Catalyst 9.9.
Here are GPU Caps Viewer screenshots: