[citation][nom]BulkZerker[/nom]I dunno, when Toms (I think) Did a scaling test with a quartet of 5770s the scaling was fine out to 3 cards, the 4th smoothed it out but only boosted performance around 20% so 5% overhead? Not too shabby.[/citation]
It depends on the game (even on settings and resolution to a lesser extent), drivers, GPUs, PCIe lanes, and more. Generally, two GPUs scale excellently with a third being hit or is and a fourth being hit or miss to make even a somewhat noticeable impact in performance.