46 gi for the road sounds very unpleasant. I ride fixed on 48x19 ( 68gi ) and 48x 17 (76gi) around Portland without any major issues, unless you plan on going up vista drive, there aren't any noticeable hills with any length to them. Hawthorne has a small steady 3-4% grade going up most of it, Alberta is flat, mississipi is another 3% grade, downtown is either up or down but very small grades.
I have a video of my commute in the today I thread and if you want to go look at that, should be on the last page or two. I also go down one of the bigger eastside hills around the 7 minute mark if I remember right.
Enjoy your trip to Portland, make sure to enjoy all of our cheap beer and food while here.