Flying fingers can be applied across the set. Check out drummers like Derek Roddy. This guy uses his fingers, probably mostly for blasting, but also for rolls. He says that he switches from fingers to wrists when one gets tired, so he can go about as fast either way.
I would say develop your wrists unless you are interested in blasting.
Anybody ever check out the World's Fastest Drummer competitions? Mike Mangini used to hold 5 of the records, but I believe he has 2 now. If I remember correctly, his single stroke roll count for one minute was 1,124 strokes. That record has been broken now, but not by much. He also had one for traditional grip and most strokes with hands in a minute.
If you have ever seen this guy play, it's really inspiring when he taps out some 200bpms on one hand, or does a perfect snare roll while wiping his face of sweat
I think there is a member here who holds a record, Matt Smith? He was like 14 when he broke a record or something. Crazy.