I installed an EVGA GTX 660 Ti in my 2009 Mac Pro 4,1 and it works great. You will need to acquire two power cables just as you will for the GTX 570. Order the GTX 660 Ti with 2 Gb of RAM, otherwise, you will need to patch one of the binary files.
To get the card working with Premiere Pro, follow the instructions published at Smoke on the Water
For powering two cards in a MAC PRO (3.1) e.g. Nvidia MAC 8800GT & EVGA PC GTX670-FTW see my post!
https://forums.macrumors.com/threads/1533504/
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