The onboard HDMI jack found on first generation 295's or on 9800 GX2's will scale to 85 hz.  The DVI port then running through an HDMI adapter has a max of 60 hz.

Newer video cards with HDMI 1.4 are capable of 120Hz at resolutions up to 1920x1080. Resolutions up to 3840x2160 is limited to 30Hz, and 4096x2160 is limited to 24Hz.