It sounds like the 266 is better for you. But it all really depends on orientation, climate, shade etc. There is no one answer. Even mixing windows on a house might be a good idea. The Midwest is a large area - could be Minn - could be St Louis. You might have a/c or you might not and are willing to spend some money so that you can continue to live without a/c. If you are predominately cold - then obviously a little more solar heat gain is a good idea. U value becomes the most important. If you have some heat - then low solar heat gain is important if you are unshaded and the windows get sun in the summer. I live in mixed and my North windows never get direct sunlight - SHG doesn't really matter there. Now my West windows - it would make sense to pay for less SHG. And generally in South windows, a higher SHG is a good idea to maximize winter heat gain. So the answer depends on too many things to say one is better than the other. But in the midwest, you probably want relatively more SHG. Not a simple subject and you would hope that your builder would have some guidance in your particular situation. If not your builder, then some energy consultant. It seems like an energy consultant (like Energy Star) should almost be standard on new construction since a lot of builders don't seem to care.

Mrschlab, Oberon476 gives some seriously spectacularly helpful information. I wish he'd come to my house and tell me which manufacturer to purchase from for my upcoming renovation and how to get what I want with my window and door impact glass :) I am currently also in the hell of LowE, clear glass or tinted glass decision-making process. The previous owners put one SGD (two 3' panels) facing north and two more SGDs (seven 3' panels). They are CWS vinyl frame LowE366 Argon IG units that were installed in 2014/2015 on the east side of our house. Bear in mind the remaining impact-resistant windows are clear glass on the west side of the house (go figure). Those were installed in 2009 (my guess from the etching on the glass, I find no permit indicating when they were installed) I brought home this luxury vinyl sample; this is how I realized the extent of the change in the color of the natural light coming in through the LowE366-laden SGDs. Because I'm choosing a specific tone on the flooring product, I don't want the color/hue/tone changed by the windows. The LVP is a warm-neutral tone, but not yellow or honey colored LVP. I wanted to see what the LVP looks like on a sunny day, so I took it out back one morning. Then I brought it inside and set it down next to the SGD (with the LowE366). Below are the results. (I mention that the LowE366 SGDs were installed in 2014 because I don't know if the LowE366 color changes with time or if the fact that they're IG units has an effect; or maybe in 2014, CWS used an obscure LowE product-- I do not know these answers.) Also, keep in mind that the phone camera and subsequent computer image may not be an exact representation of the colors, but to my eye right now looking at the computer screen, the colors are 99% accurate. The first photo was taken in the morning sun on the east side of the house in sunny South Florida through the LowE-366 SGD. The second photo was taken when I opened the door to go out with natural sunlight on the LVP and rug below it. Is the hue of light from the sun coming into the house drastically changed by the LowE366? You be the judge. (I say YES) Also, when I look at the LVP in the afternoon on the west side of the house with sun coming in through clear glass, the tone of the LVP is yet again a natural wood tone, just like you see with the door open. I did have to close the plantation shutters on the east-facing LowE366 SGDs to control the experiment so the only incoming light came in through the clear glass of the west-facing windows. Hope my pathologically detailed research helps you make your decision :) All it helped me do was rule out LowE 366 and plan on shade for my new SGDs and windows.

"northern climate" isn't quite descriptive enough. I get that people don't want to give their address on a forum but more descriptive is better. And it isn't just zip code, it is elevation. There is a big difference between CO at 10,000 feet vs Vermont at 2,000 feet - looking at a mountain. I would consider low e4 a minimum for somewhere near skiing with strong consideration for triple pane. I live in NC at 500 feet elevation with U value 0.25 windows. Code is what the builders are forced to put in the worst house - it is not a standard that you should be okay with.

While I also can't speak to quartz fading, I can comment on glass and coatings. There are three primary glass manufacturers that supply the residential window market in North America: Cardinal, Guardian, and Vitro. There used to be a fourth, AFG, but Cardinal acquired most of their North American assets a few years ago, while Vitro acquired PPG glass assets some years before that. Cardinal, based in Minneapolis, is by far the largest supplier to the residential window market in North America even though Guardian is a larger company overall. But while a US based company, most of Guardian's assets are overseas while all of Cardinal's assets are in the US. Vitro is based out of Mexico and would be the third largest glass supplier. Laminated glass is used for impact windows. Depending on the interlayer (plastic between two glass panes) used for manufacturing the laminated glass it will block from about 97% to about 100% of UV light through the window. However, as much as UV is the primary contributor to fading, visible light also plays a significant part as well. I suspect that most people are at least passingly familiar with UVA and UVB. UVA is approximately 315-380nm while UVB is roughly 280-315nm, while visible light is from 380-780nm. From our perspective, UVA is the primary contributor to getting a tan (and skin cancer) while UVB is the primary contributor to getting burned. (If anyone is curious, germicidal is UVC at about 100-280nm, but sun-related UVC is blocked by the atmosphere, and that's a VERY good thing...healthy ozone layer matters). Ordinary window glass will block UVB and a little bit of UVA. Adding the interlayer in impact glass blocks most of the rest, but does virtually nothing for blocking visible light, whereas LowE coatings will block some UV but also some of visible light as well in the wavelengths that tend to contribute the most to fading thus being the most effective choice for limiting fading short of boarding-up your windows. There are a couple of different scales used to define the effectiveness of materials at slowing fading based on UV and visible light combination. I stole this small chart from the Cardinal website because it explains the various options for limiting fading potential much better than I can.... The last two numbers in the Cardinal LoE name is the percentage amount of visible light passed by the coating. Note that the darker the coating, the more effective at limiting fading potential.