If it's like Matrox's other multi-moniter setups drag on the card/system will be negligable. Unlike other multi-moniter setups Matrox patented the best method of doing this with minimal performance drag. It actually renders the scene once and splits it up in the hardware between moniters.
This looks the same just taken to a 3 moniter system instead of 2 like before. Everyone else has to render a screen for each moniter. Less efficient that way to say the least, also less usefull.
