With Epic Citadel, we aimed for 30 fps in the general case. It is possible to run at 60 fps, although you'd have to make content tradeoffs. There is an Engine.ini value that controls the max framerate:
For 60 fps, change MaxSmoothedFrameRate to 62. You can also disable bSmoothFrameRate to let it go as fast as it can, but we do not recommend this, as the framerate may tend to bobble between to different framerates (20, 40, 20, 40, etc), which generally looks very bad.