What kind of GPU would work best with a Mac Pro 1,1? – Info Mac

Hello all! I recently got a 2006 Mac Pro 1,1. I installed two X5365s and upgraded the RAM/Storage. I then flashed it to 2,1. So now, I’m running El Capitan and need to find a better GPU for this machine that will be compatible. Right now, I have the 7300 GT. I have an HP GTX 1060 3gb laying around but I’m kind of afraid to pop it in there. Any recommendations? If the 1060 won’t work, I can always buy a new card. I was thinking something in the 600 series. Sorry for being a noob, this is my first Mac Pro / Mac desktop ever! Any help is appreciated.

TLDR: What kind of GPU should I put in my 1,1 flashed to 2,1 2006 Mac Pro?