no idea about the duke 690 wheels. I was thinking of going up more teeth on theback but i have got used to the 15 42 setup. She has enough top end to do me and still throws the front wheel in the air with a slip if the clutch in 4th.
Im using the disc of the enduro wheel (21") and so far there is plenty of stopping force. A twat changed lane last week infront of me and it got used as hard as i would like to use it without a problem.