Adding another gig of memory to this card is simply a selling point. There are many, many people who seem to believe that more is always better (1333mhz memory, 1600mhz memory, 1800mhz, 2000mhz memory etc.)
People will pay more for bigger numbers whether it means anything or not, and I have witnessed this first hand in the retail stores myself.
The following scene I witnessed in a Fry's one afternoon, honest.
Salesman to customer......This GPU is brand new! This Palit 8800GT has 2 gig of memory! Yes 2 gig! it is the most powerful card we have on the shelf right now for the money, it is only $389!
Customer to Salesman.....Really?!?! WOW!! We were lucky to come in today and be able to get one while you still have them in stock.....OMG I have to get one of those beasts!
I quietly pick up the 8800GTS G92 512meg OC card for $229 with a $30 instant rebate right next to it and walk away shaking my head in disbelief.
I would offer though, that high resolutions, high detail settings, a pair of these cards in SLI with a high end CPU like an overclocked i7 would very likely show some benefits. 2 -1 gig cards means double the raw power, but you only get 1 gig of memory, so putting a couple of 2 giger's in SLI would realize you a full 2 gig of memory available for 2 cards working together. That I wouldn't mind seeing benchmarks for, but I still think the gain would be very slight.
I don't have any actual benchmarks and I don't have one myself ( I do have the 1 gig version), but there is my 2 cents worth anyway, take it or leave it.