Prices of gtx690 is unlikely to drop with release of the gtx790, they will just become discontinued with the reales of the next nvidia x90's as previous cards have. I bought a gtx590 and sought to buy a second a year latter since the gtx690 was released to find they were very rare to obtain ( discontinued) and paid the same price as the first one after attempting them to drop the price as discontinued etc - short outcome no!
Wait for the 790 then decide