Getting a newer PSU would of course increase your ability to upgrade, but what is the PSU the system currently has in it?
Off-hand I'd say a 280-280X should be within reason of similar power draw to your previous card while besting it in just about every game. You could find one used relatively cheap on eBay.
CPU: i7 3930k @ 4.6GHz 1.29V (Corsair H110-cooled) ~ Motherboard: Asus RoG Rampage IV Extreme
RAM: G.Skill Sniper Gaming Series (4x4GB 2133MHz, CL9) ~ PSU: Corsair AX 1200W ~ Case: Enermax Fulmo GT
GPUs: 3x HIS R9 290X Reference (Core) Editions in TriFire, Max Load Temps: 71C/70C/71C during OC testing :-P