That is not true as long as its the same gpu and memroy size it does not matter what brand it is just as long as its the same card. I ran 2 8800gt's in SLI one card was zotac and the other BFG and worked brilliantly.
Earlier models were more forgiving with it, as are pure reference designs.
Most people don't buy the simple reference design models unless they are extremely early adopters, though. I have seen different brans work occasionally together, and does only really apply to 100% reference models, but it'd be foolish to tell this guy it WILL work. I've got two old 9800's here of different brand type, as well as 2 285's of different manufacturer that I simply know do *not* work because they are different brands. I've tried them, and they don't work in the least in SLI form together.
nVidia themseves say to only use the same manufacturer, so I'd rather not confuse people, heh.
Crossfire is a whole different animal altogether.
