Not much of a difference in energy savings annually. I would look for a window with as low a SHGC as you can get. I would also not select a window based on those numbers any more than I would purchase an automobile based on fuel economy. There's more to it than just energy efficiency. I would also say that based on the current state of window technology that a manufacturer who can't muster better than a .35 U-factor would have a hard time selling me on their window.

Thanks, Skydawggy. Here's the situation:
After months and months of research on vinyl, vinyl clad wood, fiberglass, fiberglass clad wood, & aluminum clad windows, I am sold on the Marvin Integrity-construction, aesthetics, warranty, the company--just wish it came in the Coconut Cream exterior color. Loved the aluminum clad, but way out of our price range. Hate the look of the vinyl (we had vinyl in last house but windows were always covered--not the case in the new house lots of windows with no coverings to show off the gorgeous view). DH did not do any of the research & only recently went to look at the Integrity line. Builder wants to get started in next 2 weeks which means we have to have an answer for him on the windows pronto.

The builder uses PlyGem Pro All Vinyl, so we have a window allowance based on that price ($13,000). The Integritys are running approx $7-10,000 higher ($7K means downgrading the options and losing some transoms, $10K gets us everything we want).

DH does not like the vinyl windows at all, but he says we're already pushing the envelope with the budget and doesn't think it makes sense to increase the budget $7-10K to upgrade to the Integrity.

This is one of those items in the build that I am pretty adamant on and I'm going to have to make a strong case beyond aesthetics. Even with aesthetics & maintenance-Mom & I just went to the Parade of Homes and saw the vinyl windows after they've been in place for a few months--dirt & grime in all the outer seals (don't know if it's a actually a seal, but it's some sort of rubber or pliable vinyl piece that abuts the hard vinyl of the sash). We didn't have those seals on our last house. I definitely don't want to have to clean that everytime I turn around (looks like you'd need to clean it with a toothbrush) & I know DH won't want to either.

So we have aesthetics and the differences in SHGC & U-Values. I've mentioned warping, fading, etc. but since we haven't seen it...out of sight out of mind, I guess & how often does it happen. What else am I missing?

The thermal data is not that far apart. As a matter of comparison, I like the higher VT and SHGC numbers for the other window.

In terms of the vinyl vs. fiberglass comparison, you can't really put a price tag on getting what you want. Keep that in mind as you will be looking through the windows for years to come.