Mirrors costing you FPS?

Look in the vehicles folder for the vehicles you want to change. In there you will find a file called mirror.bmp.
I reduced it's resolution by 50% (i.e. in paintshop pro I changed it from default 5120x854 down to 2560x427), and gained those fps!
And I could barely tell any difference in the mirror!

The mirror dimension changes for each car I think, so you would need to do this for each car you drive. I bet you could reduce it even further for still more gains.

Ok, I noticed there is no .bmp file in the GT3 Vehicles folder.
Look for the extra mirror files you downloaded with the mod/reduce the size in paint and place the file in...GT3 Vehicles Folder. It will be the only loose file in the folder. Should work fine.

Seems that if you delete all files in the Shared folder except the coreshaders.mas it fixes the problem. My frame rate is much better now.