Not really the best time, bird wise, unfortunately. As Pete says all the migrants will be hard to find now, Pied Fly, Redstart, Tree Pipit etc.
You may come across something on the moors, but they can be very difficult, particularly if you are inexperienced.All the larger bodies of water.. Carsington water , Tittesworth etc will probably be quiet too, awaiting the influx of wildfowl as we come into autumn, though keep your eye out for Osprey and waders, passing through.Still I think you will find it a beautiful area so enjoy your visit, and you should be guaranteed Dipper..if all else fails try Lathkill Dale, not far from Bakewell.As always a little local knowledge is worth its weight in gold, so chat to any birders you bump into.