Benchmarks: DiRT 3, Showdown
Dirt 3 favors Nvidia GPUs, so it's no surprise that the GTX 660 Ti managed to outpace even the HD 7950. It was also 11% faster than the HD 7870 and 3% faster than the 7950 at 1920x1200.
On the flip side, we've found that Dirt Showdown favors AMD and as a result, the GTX 660 Ti was 21% slower than the HD 7870.