This is my experience.
When I updated from 10.6.3 (64) to 10.6.4 (32), cinebench 11.5 Opengl dropped from 13 to 3.8. In order to install the nvidia gtx285 update, I changed the computer model id from iMac 11,1 to MacPro 4,1 but although the update was successful, the open gl performance did not change. I then changed the model id to iMac 11.2 to attempt the mid 2010 Apple update. The update was unsuccessful but big surprise, the opengl score jumped to 13.5.
I have just installed the SL graphics update and the opengl score is now 14.8 but on reboot I got a message that Cuda 3.1.1 needed an update. This stuff is weird but compelling.
Robt