It will probably pull down better to 24p at normal speeds, but when you do a frame-rate conversion to 40% speed, it will not look as crisp–there will be too much motion blur at 1/60.
Generally speaking, the other method I’ve occasionally used is to film at 120p, use frame-blending on realtime shots, and then at 120p 1/120 shutter, it starts getting crisp enough to work.
My vote: shoot some test footage. See if the 1/60 shutter works for you. That’s really the only way to be able to tell.