You could sold your 7850 and get a 7950 or even 7970 >
You don't have much space for upgrade since you are on a previous generation Intel processor and upgrading will cost you more on Intel side... For 300$ you could get an AMD FX 8320(180$)+Hyper 212 Evo(25/30$) and you have 90/95 for an nice AM3+ motherboard.
http://cpuboss.com/cpus/Intel-Core-i5-3570K-vs-Intel-Core-i5-2500K
http://www.anandtech.com/bench/Product/288?vs=701
http://cpuboss.com/cpus/Intel-Core-i5-2500K-vs-AMD-FX-8320-Black-Edition
FX 8320 is a more worthy upgrade if you are doing some serious multitasking, also if you are streaming, video editing... Right now you can't see the advantage of Piledriver since older games/programs were not designed to use its advantage but in future that will change, specially since more and more games/programs are multi-threaded...
http://cpuboss.com/cpus/Intel-Core-i5-2500K-vs-AMD-FX-8350-Black-Edition
If you live in area where power is 8-12 cents you can get FX 8350 that is mostly 10% better than FX 8320. But you can OC FX 8320 to a 8320 level. yea.
You can always check the alternative, in gaming i5 3570k and i7 3770k are close and if you upgrade from i5 2500k to i5 3570k there wont be a much of a difference to see expect 5-10% maximum. I am just suggesting...
If you live in area where price of eletricity per kilowatt is low you can really consider an AMD alternative, but if you live where is 14-17 cents you will probavly stay with Intel.
Also take notice that Intel for each new generation has a new socket while AMD maintains sockets for several generations and even keeps some backward compatibility. Its your choice, you got the money... I think you should wait for Haswell if you want to stay on Intel otherwise if you upgrade now and you want to switch to Haswell it will cost you more while on AMD side it will cost you less to upgrade.