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I had 6 degrees float but I think my problems were two-fold. My Fizik shoes don't allow to bring the cleats very far back. Scherritt was recommending another 10mm really. The other issue was simple conditioning. Mine wasn't really up to the level needed to be competitive over a course that lumpy.
Assuming I've done no lasting damage then both things are relatively easily fixed for another crack next year.
SPD's are the answer to Achilles problems in my opinion. You need as much float/movement as possible.