So to answer my question: About $80 per inch. My builder gave me the quote for the change, I'm going with the 42" high window. I know it will make me that much happier. The cost to change to a wider, different style window was going to be heftier (more expensive window, a lot more labor for changing nearly the entire wall's framing, etc.) and my wife didn't want casements though we do love the look. So it made the decision quite straight forward once I had a number. So thank you, all of you. I'm so glad that I know about this place because it makes it so much easier to be able to get 10 or so very informed opinions in a few short hours when trying to make a decision like this. This won't be my last crisis post by a long shot as we have a long way to go in the build, but I want to thank all of you who chimed in. It gave me the right perspective to think ahead of time so that I knew when I saw a figure if it was worth it or not. Woo! Here's the rendering, with the proper sized window back in effect.

I agree with Skydawggy that getting a good quality unit combined with a professional quality install is at the top of the list. Obviously there is no question that you want the most efficient window in the more efficient wall, and your contractor is correct when he told you that better window energy numbers do result in better performance in the more efficient wall. However, that certainly does not mean that you want a less efficient window only because you have a 2x4 rather than 2x6 wall to start with. While a good U-.32 window, properly installed, will improve your overall comfort and the energy performance of your home versus the windows you have in place, a more efficient window will improve overall wall performance even more so - the question does the additional improvement justify the additional expense? A good dual pane IG with the right LowE coating may very well meet all of your needs at (potentially substantially) less cost than higher performance triple. If you live in northern Maine or northern Minnesota, I would agree that the triple may well be worth the additional cost. But in Connecticut I would definitely consider the dual pane for the best overall value. Consider that the U-.2 triples will meet 2015 energy star requirements - but does the rest of your home meet 2015 energy star requirements? Basically, meeting a future energy star level is a non-issue. You simply want the best performance for the dollars that you are planning to spend. So, to add a few numbers: Imagine a single wall in a home that is 100sqft (for simplicity). In this example we will assume that this wall has an overall R-value of 10 (typical 2x4 construction)including the effect of studs, outlets, etc (but not windows), and just say that this wall averages R-10 across its total surface. If we add a 5x 2 (10sqft) window to this wall and this window has U factor of .32. Wall = R10 or U.1 Window = U.32 Window = 10% of wall Wall = 90sqft, window = 10 sqft, overall 100 sqft Wall = 90 sqft x U.1 = 9 Window = 10 sqft x U.32 = 3.2 9 + 3.2 = 12.2/100sqft = U.122 or overall wall R value of 8.2. Now if we change to a window with a U.20  Wall = R10 or U.1 Window = U.20 Window = 10% of wall Wall = 90 sqft, window = 10 sqft, overall 100 sqft Wall = 90 sqft x U.1 = 9 Window = 10 sqft x U.20 = 2.0 9 + 2.0 = 11/100sqft = U.11 or overall R value of 9.1. So, changing from U.32 to U.20, in this example, results in an improvement of 63% in window performance, but it also results in an improvement of 11% in the entire wall structure  the higher the percentage of window sqft in the wall; the more the overall R-value improvement if using the lower U-factor window  in this example assuming 10% window coverage in the wall. If your wall is 15% of the total wall area then the improvement to entire wall energy performance will be increased proportionally. By way of comparison to a 2x6 wall (per your contractor)- which I am going to say is R-20 because the math is really easy (being lazy here - but it is close enough for this illustration): So if we change to an R-20 wall we have: Wall = R20 or U.05 Window = U.32 Window = 10% of wall Wall = 90sqft, window = 10 sqft, overall 100 sqft Wall = 90 sqft x U.05 = 4.5 Window = 10 sqft x U.32 = 3.2 4.5 + 3.2 = 7.7/100sqft = U.077 or overall wall R value of 13. Now if we change to a window with a U-.20: Wall = R20 or U.05 Window = U.20 Window = 10% of wall Wall = 90 sqft, window = 10 sqft, overall 100 sqft Wall = 90 sqft x U.05 = 4.5 Window = 10 sqft x U.20 = 2.0 4.5 + 2.0 = 6.5/100sqft = U.065 or overall R value of 15.4. Or a potential 18.5% improvement to overall wall performance with the higher efficiency window in the higher efficiency wall (assuming I did all the math right..it is before breakfast on a monday morning...).

Thanks for your thoughts, @millworkman. I understand the Essentials is fiberglass interior and fiberglass exterior. I have not really looked at that because we would like a stained wood, traditional looking interior which is what we have currently. Our house is a colonial style cape. I did see the Elevate which has the wood interior with the fiberglass exterior. I did not like the wood lip at the top of the bottom sash of the Elevate...felt it was a bit contemporary looking. I don't know of any others in our area (NH) to consider at this point (have looked at Harvey Majesty, Pella LIfestyle, Andersen Woodwright, Andersen 400 series Tilt Wash and the Marvin Elevate). This is what we're trying to replace (Pella Originals circa early 1990s):

When evacuations are ordered, you aren't supposed to have to go far. Just get out of the storm surge/flood zone. If you have no other options, go to the local hurricane shelter. It's not pleasant, but you'll be safe and have company. I've had to do that before and it looks like I may again this time, because the roads will be full of crazy panicking people who should have stayed closer to home, so I don't expect to be able to leave the area, even to get to Orlando, which is normally about 2-1/2 hours from here. However horrific wind is, it's mostly water that kills people in hurricanes. I had a lot of friends who spent Andrew hiding under their couches or crouching in their bathtubs while their houses blew away, and except for the trauma of it, they were fine afterwards. The very worst thing is to be stuck in heavy traffic with a storm bearing down on you. Gas is already in very short supply in most of FL and I worry that a lot of folks are going to find themselves stuck up mid-state somewhere running out of gas with no more available. If you want to go, leave as soon as possible, but remember that you aren't going to automatic safety unless you head for the midwest or something. I was considering that after the storm I might go up to a lodge in the mountains in NC where I've stayed before, but you know what? The models are starting to show Irma making it into that area, too. For sure if you've never done this before you should try to find a place where you will be with other people.