I have those, and I just bloomed an amarylis for the 1st time :) I see no negative impact upon my orchids in that window (NE for me) but most of mine are under fluorescent lights in another room. All of my plants in the bay window with the windows as you describe, thrive and love it there.

I believe it is, but I also have always found Pella literature and catalogs confusing. What are the U or R value numbers on some of the windows, that will tell a lot. Numbers around an R-value of about 0.3 +/- indicate low-e. No low-e would be about 0.5. Virtually every window manufacturer uses an argon fill in a low-e window, so that should almost be a given. Of course, if you have internal shades in your Pella, the operating knob passes through the glass pane and the argon gas can't be sealed in, those would not have argon.

My LoE 272 windows replaced Pellas that had no UV coating (as an aside, don't get Pellas, avoid). I have not replaced all my windows (too expensive), but am replacing them a few at a time. So I can compare them since I currently have both. I have several very large windows that let in a lot of light, and there is no problem with that. I do not see that the glass is darker. I definitely notice less burning and sun bleaching my furniture and no longer overheating my south-facing rooms. I will say that my house plants that need a lot of sun have not flowered or grown, even though I was assured the LoE 272 would not affect them. My plants that need less sun like my African Violets are doing well. You should really speak with your contractor too since it sounds like he has proposed LoE 366. My contractor told me our climate doesn't need that though he would have ordered them if I asked.

"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.