The most notable climb on the Orro Sussex Downs Classic is Kidd's Hill. Kidd's Hill is perhaps nicknamed The Wall because the road appears dead straight. So from the bottom you just see the hill rising in front of you. The gradient is pretty steady, though it gets steeper as progress 2/3 of the way up the climb, just before easing off in the last 100m.
You can find out more about the Orro Sussex Downs Classic Sportive and enter the event via:
Orro Sussex Downs Classic Sportive
UK Cycling Events: https://www.ukcyclingevents.co.uk
Cycling Weekly: http://www.cyclingweekly.com