Welcome to the forum!
DS didn't sit for Sutton so I can't comment on that but I think the hardest thing was keeping the motivation going for the 4 months between WCGS & Wilson's. Fortunately (IMO) for your DS, the exams have been moved for next year and are much closer together - having it right after Xmas was really tough for DS as we had family over from Oz (all very bad timing!
). However, some may consider this a disadvantage as if unsuccessful with Wallington, you still have a few more months to prepare for Wilson's. But in our case, as DS passed Wallington we lost the incentive a bit and were rather too relaxed for Wilson's!
Good luck with it all - I don't envy but hopefully it will all be worth it in the end!