I also got fluctuating framerates and I'm running 2 GTX560Ti in SLI, although occurred a few times and was like a 1-second framerate drop.

GTX560Ti can still keep up with the latest graphics-intensive games, that I even held back on upgrading to GTX760. It's just that some maps with players or going to another map (which tends to render graphics on-the-fly since some maps are freakin large) tend to drop framerates. Oh yeah, I also got li'l bit of dropped framerates in Skyrim, but not that much.