Heres a good tutorial on how to use Motion (a program that comes with Final Cut Studio) to further slow down your footage. The video stretches 60 fps footage to 1000fps using a setting "optical flow." Just an alternative to twixtor.
to me it kinda looked a bit fuzzy. especially the last shots. Not sure if its my computer. It does look good but i prefer premiere pro over final cut but then again i havent used final cut all to much.