CrossFire: Battlefield 3 At 7680x1440
Radeon R9 290X scales well in Battlefield 3. A win with one card turns into a win with two, even if both hardware combinations manage frame rates that appear plenty-playable.
Charting frame rate over time shows that AMD's advantage comes from the beginning of the benchmark, inside an aircraft carrier.
A CrossFire'd configuration does incur higher variance, though. Here's the thing: it's subjectively really hard to tell the practical difference between two Titans and two R9 290X cards in this game. There is clear tearing and stutter from both solutions, but this is a persistent issue with Battlefield that I'd chalk up to DICE's engine, rather than a multi-GPU technology.