Tough call. JFK-LHR on a 777 is never worth 30k if you can get the bulkhead (17A,B are the best E+ seats in the fleet). IAD-MUC, being nearly 1.5 hrs longer and having an inferior E+ section, might be worth it. Your call. If you want to use your miles for a real award keep in mind that savers in F are going up to 120k and 140k (Europe and Australia, respectively) in a few months. So only you can decide how you want to spend your miles and if you feel that C is that much better than E+.