well i have a XFX GTX280 and i've been watching a BFG Tech GTX280 on craigslist. well the guy has dropped the price to $250 from $400 and i am thinking about buying it and doing some SLI... thanks for the reply.
yes two brands would work together, and then no to two different cards. But remember, that if one card is clocked lower then the other, the higher clocked card will downclock to the speed of the lower clocked card.