I did a similar build a few months ago. Bought a used Rampage 3 Extreme for 120€ and a Xeon X5560 (2.80GHz Quadcore with HT) which i got for 35€ overclocked it to 3.43GHz (probably could go higher with better cooling) used the rest of my last build
-Evga GTX 780ti SC (which i also got used really cheap for 320€ with an EKWB Watercooler installed)
-8GB Crutial Balistix Sport RAM
-250GB Samsung 850EVO SSD
-1TB WD Green HDD
-Creative Soundblaster ZX
-Coolermaster Silent Pro M2 720W PSU
and depending on the game it's about a 20% FPS increase over my FX 8150 @4GHz
Peronally i would recomend anybody to use a second hand X58 Xeon for a budget Gaming build
I haven't looked too hard at the 7 series numbers, but it might be worthwhile to just get a 770... its pretty much a beast. and single cards do usually just work better than SLI for the reasons Owen said before.