The Chapel Gate – Roych – Hayfield – Jacobs ladder – Edale loop is a classic for wet conditions as it’s quite rocky. Comes up quite modest on the mileage, think it’s only 15 or so, but it’s a hard 15 for most.
Can easily add extensions for a longer day – Some variation of the Ladybower trails in the afternoon, for example.
Not the OP, but we did this on Sunday, based on the Vertebrate link above. I added in a little diversion down to Birch Vale and then had a potter alongside the river to Hayfield before climbing back up to Jacob’s Ladder. It made it about 17.5 miles rather than just under 14 for the original route. Great day* out.
Well, half a day really, but it took 4 hours of driving to get there and back!