You're reading my mind @CXRAndyGood luck Carl,
Dont go full bore early on, If you get an early start group(try and leave before other CC-ers). Try tag onto groups of geared riders then drop off until you find a group which you can maintain a comfortable cadence without blowing up. Have you been out on the SS to see how your legs and cardio feel over climbs which are 2 to 3 mins in length at a decent pace? That's what the climbs are like
Your gearing is about the same as mine, so good to know it's a suitable gear for the areaI ride around that area quite often on my Burls 48x18, there's no really steep or long drags, maybe a mile at 2.5%. The fens are far more likely to be the problem, if there's a good breeze blowing find a large group and stay at the back ;-)
anything over 10% for more than a few hundred metres