What's the longest butterfly race you could swim?

Following Creampuff's logic, I picked 50m. Anything longer than that, and my stroke isn't really racing, it's more 'mellow mode' (I have completed up to a 200 true fly). As for how long I could swim fly... using USMS rules and a breaststroke kick, however long my knees hold.

Following Creampuff's logic, I picked 50m. Anything longer than that, and my stroke isn't really racing, it's more 'mellow mode' (I have completed up to a 200 true fly). As for how long I could swim fly... using USMS rules and a breaststroke kick, however long my knees hold.