Lowe's Pella vs Home Depot Jeld-Wen

I'm going to be replacing some windows in my house, and recently obtained 2 quotes from the Big Two DIY mega stores. Lowe's quoted me about $1000 for the configuration I want, using Pella's 25 series. For the same configuration and features, Home Depot quoted me $600 for the Jeld-Wen Sierra Side Load series. What gives? Assuming proper installation, is there a quality difference that would account for the pricing? I live in Seattle, and while it can get 'chilly' here our winters are not extreme by any stretch.
Any help would be appreciated.

The Jeld-Wen Window is a better window. They both have equal energy ratings. The fin on the JW window is a dual wall on retrofit windows and holds up better in the heat against the stucco. ALso the warranty is better on teh Jeld-Wen window. Lifetime to home owner who buys the windows as long as you live in the house. Pella is a 20/10.