If your power supply can handle a high-end GPU and has PCI-E connectors, you should wait for the boxing day and see the prices. At the moment, GTX760/770 can handle pretty much every games that I know of with very good performances (along with a good processor and sufficient RAM, of course), and the 800 series will likely be very expensive when it gets out.
If you can wait to play the newer games until then, then I guess waiting wouldn't hurt. By then the 760/770 prices might come down some. But don't wait for the next series just to get the newest thing because the next newest thing will always be around the corner.