So by my count your route has the following categorised climbs:
Adlington to the top of Brickworks - cat 3
Pike Road - cat 4
Pym's Chair - cat 4
Goyt Valley - cat 3
Mam Tor - hilarious looking cat 3
Eccles Pike - cat 4
Whaley Lane - cat 4
By my reckoning we'll climb about 3000 feet in the first 25 miles, then there's about 30 miles of downhill and fairly rolling countryside, then about 15 miles with close to 2000 feet of climbing, and then we pretty much roll downhill back into Stockport.
I'm thinking we - and by we I mean I - will need to conserve energy on that middle 30 mile section, when it will be tempting to go too fast, or there is no way we - and by we I again me I - will enjoy the cat 3 at Mam Tor if we make it up at all!
Also, FWIW, I've plotted the route on ridewithgps and it comes out with 6500 feet compared to your route on Strava at 7500, so who knows!