Looking at the AnAnd review, they really are on par with each other. In most cases the 1950 was either 1 FPS behind, or more than 5 ahead in some games.
Being that I found you a reasonable, retail, in stock price I found you at ZZF, I suggest you read through
THIS review and see which games you like to play best. And the fact that ATI can do HDR+AA in Oblivion.
The 1950 also doesnt have the hassle of the rebate.
Also, dont forget that 7900gt's can be voltmodded to increase their performance to about a 7900GTX. You may want to look into this.