Video RAM & Photoshop CS5

I'm running Photoshop CS5 on a Win7 64-bit machine with a quad core processor, 8Gb RAM and a pair of nVidia 9800GT video cards with 512Mb each, in SLI mode (which supposedly allows games to utilize the two cards in parallel.) I do not see any advantage to CS5 from the SLI mode, and realize that Photoshop is only utilizing 512MB of the video RAM.

I am about to remove one of the video cards in order to be able to use the small PCI Express slot for a USB3.0 adapter. The slot is unusable while both video cards are plugged in.

The choice I have is between leaving one of the video cards and use 512Mb video RAM for Photoshop, or to remove both cards and utilize one PCI Express slot for a card with 1Gb of video ram. Would the extra 512mb make a noticeable difference in CS5, such as faster rendering or generation of previews, etc? Or, at this time, would it make more sense just to leave one of the cards in with 512Mb?