New construction actually means "new construction". This is when the house is framed and sheathed, and the windows are mounted in rough openings with 'installation fins' or 'nailing fins', prior to the siding being applied. If your talking about replacing windows in your house, and if you use new construction designed windows, you'll most likely spend a lot of money on a lot of extra work involving alterations of opening sizes, siding, and fitment issues. I am merely correcting your terminology. If you live in an existing house and are replacing the windows, you will want to use replacement windows because they are accurately custom sized to the existing openings. They will be installed either as inserts or as complete tear-out "full frames". The insert and full-frame will be the same window, just different installation methods. The full frame will replace everything back to the studs, including interior and exterior moldings. The full frame may have a modified jamb to receive sub-jambs, or full frame may be inserts that are sub-jambed in the same way, but with the standard jamb. An insert will be installed in the existing frame, preserving existing moldings. Or it may be installed in a sheetrock return opening either on top of the sheetrock, or to the studs with a sheetrock cut-back. With both methods, the outside trim can be wrapped with colored sheet aluminum custom bent to fit for a maintenance free exterior. High performance vinyl will most times cut down your glass area unless you do a full tear-out and re-trim. Hope this makes sense to you. I thought it might help you as you talk with window companies, contractors, to use correct terminology so they understand what you're talking about. Hope this helps.

First, thank everyone for the speedy responses, your insight is very helpful. Seems like Okna 500 is definitely the preferred option. I have a follow up question. I am in between Okna 500 vs. Interstate 8800. Interstate is definitely smaller and less known. Can anyone comment the difference between them is substantial? The price differential is ~$50 per window with Okna being more expensive. Thank you!

Not being "like for like" does not necessitate new construction. You are dealing with an empty opening whether you are installing into a buck frame or a rough opening. Replacement style is a nice choice for most people. New construction (full tear-out) is a better choice when you have existing water management issues, substantial structural frame damage/rot, or you are very concerned about the potential loss of glass area. The pros of replacement are cost ( typically a couple hundred + ), your interior woodwork is not disturbed, and a far less intensive installation. Did I mention that there is a MAJOR cost difference? ;)

Find another dealer. I have always considered replacement windows as something that is made to fit in any frame. Unless the frame size is the same for both your current and new windows, I don't see how they would fit. Perhaps the wide blinds won't fit because the new window is wider than the old window (mainly because all new windows these days are double glazed.) As for LoE, it is a coating that lowers the heat transfer and retards the solar heat gain (i.e., the sun coming in and heating the home - which although good in the winter is very bad in the summer.) The glass manufacturer is probably Cardinal, which makes a number of LoE glasses - 240, 270 & 366. The last two digits are the visual light transmittance in percent (the lower, the more shading.) The 366 seems to be the best glass for any window that would get the summer sun, as it has the best solar heat gain retarding with a good light transmittance (good for east & west.) The 270 is the cheapest, but has low solar gain retarding (good for the north, or south, if the eaves are long enough.) The 240 is almost like a tinted glass, and nowadays is really only put in by cheap contractors who don't want to pay the extra for the 366. Argon or Krypton (or any noble gas) lowers the heat transfer even more - but not enough IMHO (at typical dealer prices) to make it worth it. Besides, evidently the gas bleeds out after a few years, being replaced with plain air, which is about 3/4 Nitrogen and 1/4 oxygen (both diatomic molecules which result in a higher heat transfer coefficient than the noble gases.)