Avenue Rd north from St.Clair is fine. Jedburough/Duplex is sloooow. I believe from Davisville to Old Yonge there is a stop sign on every side street. Literally.

I aslo used to take Don Mills to Finch last year and found it to be a decent north/south route. Most people followed to bus/taxi/bike lane rule and I never had any problems riding Don Mills at 7:30am and 3:30pm. Not much scenery though.