The key indicator around here at least (being a really cold winter climate zone) is how well do the windows insulate. The window can be built differently but I’ve defaulted to triple pane only following some painful experimentation. For 90% of the year double pane will be ok (for Canadian made windows) but for that cold deep winter phase it just isn’t good enough. At that point any client will be really grateful the builder added triple pane windows and absorbed the cost at the time it was specified. This is impossible to retrofit later without major cost and trouble. The window is labelled for its energy performance by the manufacturer. The metric they use is the U factor which is a unit of watts per meter squared kelvin. This is heat loss and the lower the number the better the window. But we want it in imperial R value where a bigger number is better. So we convert metric to imperial by dividing by 5.678 and then take the inverse of that to get your R value. These windows work out to R 4.9. I’m guessing this is taken at the centre of glass and the frame may be less. Regardless this is a good spec. R5 is equivalent to 4 inches of wood or 1 inch of dense styrofoam.
The r4.9 window. Well worth the additional dollars purely based on interior comfort in winter.