I'm interesting why we don't have acces for any of these functions on HD2900 cards? As I remember on X1950 we had Fetch4, which wasn't avaiable in OpenGL (but maybe it was avaiable in ogl and I'm a wrong?), but was very nice feature. I don't think so this feature was cut from HD2900 hardware, so why AMD didn't offer support for this feature in Catalyst drivers? I know that GL_ARB_texture_gather require full DX10.1 support so units in HD2xxx may be not full compatible with specification of this extension, but GL_AMD_texture_texture4 was introduced by AMD, so I think that they can adopt this extension for HD2900 specification, but they didn't it. Why?
the rv670 and rv7xx supports "textureGather" but does not support "textureGatherOffset", which is only available on r8xx+. so we exposed the extension for those older ASIC with a min/max offset of 0, so that the rest of the extension can still be used.
unfortunately, r600 was left out and we have no immediate plan to change this.