Nothing wrong with vinyl in really cold climates. Matter of fact, most of the upper end performance lines are made in vinyl. Can you get some thermal and structural data on the window?

Just had the Pinnacle series (extruded aluminum clad windows) casement windows installed in my house. It does NOT perform any better than my 30 yr old original window. The owner of contractor company came out to look at the install and agreed that there is air leaking in thru the sash and the sill. A technician from Windsor Window agreed as well. Then a regional sales manager came out to look at it, and he basically played dumb and said he's not feeling any air leaking. The sales manager basically came to say they are not going to help in any way. Each window costed me $1100 (just the window not including labor), and the quality of product delivered is not worth $1100. There are scratches all over, and some of those are pretty deep that they are going to show even after painting. If there is anyone evaluating Windsor Window, based on my experience I strongly recommend you stay AWAY from Windsor windows because they are not worth the money. Luckily, I only replaced my bedroom windows upstairs. I will NOT use Windsor Windows again for first floor and my future home.