Okay, who asked you to plan a route over Sutton Bank? why?
I would go back to that particular person and say I prefer to avoid active gliding sites, I am not a glider pilot, and do not understand their requirements or activities. Why not vector me over an active military danger area instead? there's less likely to be any activity!
Though of course if it is pissing down with rain, or fog, and you are IMC qualified, you may be able to fly at an MSA to avoid the interesting folds of the landscape in that vicinity, and not be upset by any of the challenging wave activity that can be found downwind of the uplands....
Sutton Bank is an active gliding site. Trouble with your average spamcan pilot is he or she is typically spending more time looking inside the cockpit than out, navigating with the latest gadgets, monitoring the gauges, talking on the radio, changing frequencies, and making sure the skid ball is in the middle. The average glider pilot on a good day is to be found in gaggles, under streets of cumulus, dolphining to use best lift. And some distance away from the gliding site. On a not very good day, the average local glider pilot will be working the ridge to stay airborne, following the rules of ridge soaring. Are you acquainted with these practices?
Best of all, before you decide on your cross country flight, why not visit Sutton Bank by road, they are really nice people, and have yourself a glider lesson. It can do no harm, and may indeed broaden your horizons.