Video card Upgrade Please Help? Gtx 760 or Radeon 7950?

Hello, I currently use my computer video card you want to get.
I think ''Msi / Asus Gtx 760'' and'' Sapphire Radeon 7950 . Which one should i get? Which is healthier work?

My system is 10.9.1. Please help

My video card is Gt 120


Mac Pro 4.1 Early 2009
8 Core 2.26 Ghz Nehalem
8 Gb 1066 Mhz
120 Gb SSD