I have implemented multisample frame buffer objects via the EXT_framebuffer_multisample and EXT_framebuffer_blit extensions. On my dev machine containing a nVidia geForce 8800GTX it works great, no error messages and I can antialias up to 16x.
On our target machine containing a Quadro 5600 however, I get no errors, but am hitting an apparent software path as the frame rate is about 0.1 fps, regardless of how many multisamples I am requesting ranging from 1 (min supported) to 16 (max reported support).
On another dev machine with a 8800gts, it runs fast at 2x, and slow at anything above. I do get MAX_MULTISAMPLES, and clamp to it, so the driver seems to be reporting support for 16x, but then kicking to software.
Any advice from you nVidia guys??