Would it be better to SLI two 256MB-8600 vid cards or to use one 640MB-8800 vid card?

Would it be better to SLI two 256MB-8600 vid cards or to use one 640MB-8800 vid card?

Two 8600 256MB cards within SLI, as most games are developed for a maximum memory footprint of 512MB. Also, if you are looking to do next gen video decode, the 8800 is not capable of it, as it is base on Nvidias first gen Purevideo HD engine, while the 8600 card feature HDCP decryption over dual-link, DVI enable them to display the new video formats (HD-DVD and Blu Ray) at their local resolutions. AMD/ATI just relased a up to date video card capable of this as economically, and it smacks the 8600 in benchmarks. You may want to consider the ATI Radeon 2900 XT also. Below is a review of it.
using sli give double the bandwidth so i recommend it
I would use the one 640MB-8800 card but I didn't know the made 640s. But yes use the one 640 because it won't have to run through both even though this simply creates a very small amount of work i.e. hardly noticable.