In reply to BnB:
> Hi. I reckon 40m is the perfect length for gritstone cragging, long enough for any pitch and belay
Might be pushing it for some longer routes at Millstone where you may have to go all the way back to the fence to make a belay, although if you have some long cordelettes I guess you'll manage. Otherwise, I agree 40m is decent for gritstone.
(check route lengths and belay points at Dovestones Tor and Shining Clough as well though)
I would personally take my 60m single to the aforementioned 3. "Just in case"