Love the new window thing. It's nice, enjoying the quieter house. Too, I even noted an immediate difference in how the sun affected the house at each window.
Then there is the fit thing. I measured and bought the standard size. It didn't quit fit, so I had to pull out the siding sander and such to knock off about 1/8" or so. Now and in the future, standard, for example, 3'x4' windows will fit.