For the record; window technology has come a long way in the last few years. Here are some points for all you window replacement shoppers.
ARGON: is the oldest, twice as dense as air, and twice as good at insulating. late 80's
KRYPTON: newer, 4 times as dense as air. mid 90's
DELTA-8: newest, 8 times as dense as air, twice as good as Krypton.
Low-e: the more coats the better. Triple pane allows 4 coats. Double pane only allows 2 coats.
spacers: BR-50 is the best proven in the labs over time with great temperature swings. This keeps the gas in the frame. anything else will leak the gas a just a few years.
Frame: Vinyl by itself is not structurally sound enough for any width over 26 inches. Metal reinforced vinyl is the best, better than wood.
good luck hunting. check into Oxford windows or Bristol...