Update my GPU

Hey guys, I want to update my rig so I can play GTA V, BF4,etc. at high or ultra settings. My rig:

Motherboard: P6T Deluxe V2
CPU: i7 920 OC @ 4Ghz
GPU: ATI HD 5850 OC @ 850/1200
RAM: 6GB G Skill 1600 8-8-8-24
Monitor: 24''
PSU: Corsair 850W
Case:HAF 932

My budget is ~300€

I think all is fine but GPU and RAM. I am looking at SAPPHIRE TRI-X R9 290 4GB GDDR5 OC(UEFI)

And update RAM later to 12GB or somewhat

What do you guys think?

Update my GPU