Yep; without Gallium3D our comment that we thought open source 3D could fairly easily get to 60-70% of fglrx performance would be pretty lame. The last 30% will be hard though and I don't think anyone will bother; about half of the difference comes from a very sophisticated shader compiler, and the other half comes from constant bottom-to-top tuning and optimizing of the stack, from the GL API down to the bottom of the memory manager and command submission code.
That said, if you can run a modern GPU at 60-70% of fglrx performance you're probably gonna be CPU-limited on anything but a CAD workstation app anyways
