In reply to Brendan Rose:
Lots of great Ideas!
The Hebden Bridge to Hunters Bar is a classic point to point of around 50 miles and highly recommended. Easy to do via public transport too.
It can also be done via Castleton too if you are not Sheffield based.
The Derwent Watershed is the ultra classic hardish route in the Peak district of around 42 miles. I've done a solo version from Hunters Bar and back (62 miles) which ups the difficulty is somewhat significantly
If transport can be arranged then the Full Eastern Edges from the Woodhead to Ambergate, is although straightforward but an interesting classic route of 45 miles...
And then there is the 6 Peak District Country Tops from Crowden to Buxton. 53 miles and hard all the way. The big issue is arranging lifts.
So many good ideas out there!