FCP X 10.1.1 supports better on GeforceGTX 680 or Radeon HD 7950 ??

Hello,

I am having problem with ATI 5870, 5870 became very slow after FCPX 10.1.1. specially background task, also playback (drop frame)problem when use Fxfactory plugins like photo montage, pixel studio films etc...It is not hard drive problem. I am using Mini-sas and getting around 500MB read and write.

Any suggestion please?

thanks

Mac Pro 5.1 mid 2010

2x 2.66Mhz Processor 12core

Memory: 20 GB RAM

Graphic: ATI RADEON 5870 1 GB

Hardisk: 12TB Mini-SAS ( STRADOM) with Highpoint 2277 card (speed test 495/MBS on RAID 5)

Blackmagic intensity Pro HDMI