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Another way of looking at the lighter shoe over a marathon distance is 26.2 miles with minimum support could lead to injury. Over 5k this would not be an issue. A general rule I have read is that skinny, small frame runners can get away with light shoes in a marathon as there is less load going onto the shoe support. Also the lighter race shoes have less total mileage in them so should be just worn in and relatively new for a marathon.
I would happily do a half in ASIC gels and for the last 2 marathons have been set to wear them only to change my mind on the morning. Probably due to pre race niggles putting me off. Next year could be the time.
Very individual thing......also need to take into account gait and cadence. If you're heavier and tend to 'lollop' along with big thumping strides and a 150 cadence, that's very different from a 'pitter patter' cadence of say 180-190 with your centre of gravity ahead of your knees and feet (chi-running/POSE style). Difference in load is enormous.
Anyway, all that said strained a ****ing calf muscle on a 12 mile tempo run yesterday, so potentially out for a bit including Velo looking unlikely. Grrrrrrrrrrrrrrrrr.