i use fraps - because i had the impression, that it provides the best performance among those screencap tools. you still get "ok" fps with fraps on my machine. other tools just made playing impossible.
my fraps settings: resolution half-sized and 50 fps
I use 50 fps because fraps seems to limit the framerate completely to the settings u make. i mean, the whole game runs at max. 50 fps if u set 50 fps in fraps. I usually dont reach the 50 fps when recording, its more around 30-40, but thats more than 25 (=smooth playback) and way smoother to play than a setting on 30 fps.