Hmm I'd say it depends,Are you going for a relaxing day to experiance Chessington at Halloween, or just to get loads of rides done ?For 6 hours I don't think it's worth getting an Ultimate Express Pass, the first hour at least, even on Halloween, is pretty quiet, and if you plan well can probably get another hour with small-ish queue's, so that's only about 4 hours use you'll get out of that Ultimate, 2 7 ride Express Pass' will be just about enough I reckon