can you sli with different brands

Yes it'll work. The only requirement is that you have identical model chips. Both those cards are GT's. You'll be fine.

NOTE: keep in mind that manufacturers all clock their cards differently. So take note of what clock speed that Pixelview or XFX is. Ideally, you want to have the cards running at the same clock speed- though this is not required because nVidia's drivers will automatically adjust clock speeds to match.

-mpjesse