I just reinstalled cause I was having a similar mouse issue. nagu's advice is what fixed mine. You must remove the existing video kexts.

Installed iPC with nvidia mac pro (no injectors!)
Used kext helper b7 to fix my wifi (also created /Backup Extensions)
Downloaded the 9f23installer.pkg
cd /System/Library/Extensions
sudo mv GeF* /Back*
sudo mv NVD* /Back*
Run 9f23installer
Use osx86tools to add the EFI string
Reboot -f -v

No more mouse lag! Both screens on my 8800gt 512mb card are working at full res.