When using odd groupings such as 5 or 7. I sometimes find it easier to count one hand. Example if i was doing a fill around the drums snare-tom-tom-floor tom and i was using a grouping of 5. i would count just the one arm making 3 right stokes then 3 left strokes and filling in the other 2 strokes with the opposing limb appropriately.
R L R L R L R L R L etc notice how there is 3 Rights and 3 Lefts This makes subdividing pentuplets as easy as subdividing trips.
and the same thing applies for groupings of seven except you would be counting 1 2 3 4 on each alternating limb.
Don't know if this will be overly helpful as it is more often preferred to use double strokes when doing these kind of fills. But from time to time you can use single strokes to achieve the same thing.
Another good excersise with double strokes this time. is alternating accents every 6 strokes Rr ll rr Ll rr ll Rr ll rr Ll rr ll
makes for some nice sounding fills also.
Anyway thats my 2 cents
I hope someones finds a couple of these ideas a little useful. thanks keep drumming