I have Simonton Pro Finish windows as well. I think by modern standards, they are horrible windows!
Single hung windows were installed in my home during its construction. In the winter months, it seems that if there is a wind greater than 10 mph, I can feel a significant draft coming from the side channels and from between where the bottom and top window units meet. It is probably a result of contraction of the windows due to cold temperatures....I'm not sure. Either way, I feel the windows are sub standard and I am willing to take part in a class action law suit. Anyone interested?