I'd choose the 500 ;P ... Seriously, if you are just going white or almond and you don't care about the metal handles, I think that the 500 offers the best bang for the buck. There are some structural differences as you go down the line (look at the DP and AI ratings) due to thinner extrusion, etc, but the 400 is still a very stout unit. If you can't afford to do the whole place with the 500, you still won't go wrong with the 400. It may be Okna's entry level, but it is still in the very upper echelon of vinyl windows. Whichever option you choose, go for the deluxe (DX). Adds foam in the frames and sashes and locking screens on the Dh's.

+1

The 500 is my favorite offering and probably the most popular window that we sell, hands down. Great blend of performance and value.

PJS755, Are you in fact finding that the Okna 800 is twice the price as the 400, as one might deduce from your "whole house vs half house" description of your decision making? In any case, good luck - Okna is a stellar performer based on my limited research.