So the reason I'm hitting 100fps - which is unusual - is from using Fast vcync on my nVidia card. It basically locks the screen from tearing, but does so with little to no hit on the GPU. I'm using a mid-range GTX 745 that shipped with my Dell XPS system. With vsync on I get some stutters or pauses in game play. I personally think it's due to my ancient monitor which runs maxed out at 1680 x 1070. The refresh rate on the monitor is 59.8 mhz - so whenever my FPS dips below 60 to say 58, I get a micro-pause in play. So with Fast vcync, I can build more of a buffer and when it dips, I don't see any visible pause. Just one of the little quirks I've had to iron out. UE is much smoother though, but being paranoid, I haven't dared touch the settings from what was working before.
I average between 45-65 fps most of the time, though! I don't want you to think I have some sort of magic trick working over here!