I was running it fullscreen and no, it didn't have even 1fps more than running it with one card, so no, I did not have constant 60 fps. If SLI was working properly, then I'd have full load on both GPUs, just like I had with other games.

Again:
1x260GTX: 35fps@99%load
2x260GTX: 35fps@54%load

-> game not scaling

Since ARR will have fixed fullscreen, as promised by YoshiP, they should also work on making this game scale beyond just splitting workload without increasing fps.

SLI also works in windowed mode btw, I think it's because it's using multiple gpus even on desktop.