Have you retested for your FTP in the aero position? Lowering your FTP 5-10W from a FTP would not be on the safe side in many cases. Unless you are doing a majority of your rides in the aero position, and able to hold it for 3-4 hours without any problems people see upwards of 10% reduction in power while in the aerobars. You said "on the trainer I never rode aero"... what about on the road? What is your comfort level on the road in the aerobars, how long can you ride in the aerobars without getting out, and how long have you been consistently training in the aerobars on the road? I think more important than what wattage to hold +- 5W is going to be your ability to ride in the aerobars for the entire race. Maybe I am wrong though. You have posted some decent results in other races, were you able to stay in the aerobars the entire race?
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