This isn't strictly the Peak District but it's very close. I rode this climb yesterday and it's a cracker.
2.3miles long with an average grade of 7%. It starts off steep and feels like a series of ramps and then a bit of a drag towards the top. I combined it with a climb of Star Bank and both of them are pretty testing.http://www.strava.com/segments/2579057
My faves are blaze hill to pyms chair, the other side of that hill which is 'the street' and Holme Moss. Oh and Marple to Mellor.
I live North end though so haven't explored the south too much.