I'm a bit out of sync with current video hardware so I hope this question doesn't put me in the "noob" category.
Okay, so I'm slamming an Alienware box together and I'm trying to figure out whether it would be better to go with a dual NVIDIA GTS 240 SLI or a single 260 GTX video solution. I do some gaming, mostly flight sims, and will be using Windows 7 and Linux (probably Ubuntu or Slack(KDE)) without wanting to recompile kernels, stalk Linus, and sacrifice cattle to the video driver gods.
I always, always, have always said, even when Tom's said different, it is better to buy the single fastest card you can afford. Then add another later when you feel performance starting to slip, and the card has gotten a lot cheaper
It's memory bandwidth that matters more than the amount. The GTX 260 has DDR3 but it has a memory bus of 448 bits which is MUCH larger than the 128 bit bus of the GT 240. DDR5 ram can't even come close to making up the difference. The GT 240 is overpriced and shouldn't really be considered until the price comes down. So is the GTX 260 for that matter. Have you considered ATI cards? They are the better choice in terms of price/performance as well as features in most price segments at this point.