I really see no need to go to a Magnum product. These are generally used in commercial type buildings when huge double hung's are required, ie over 60" wide and 7 or 8 feet tall. Your job does not sound like it needs Magnum DH units, just large standard units.

Ah - see, these are the kinds of things I don't know. I was really just intrigued by the 66" width as I hadn't seen anything that wide before and the idea of one instead of many seemed worth looking into.

I would suggest that you may be looking at an appropriate product in the "Magnum", if you decide to place one single double hung window within your wide opening. The reason that this series/type of window (Magnum) is made available for commercial openings is due to the fact that commercial openings are predominantly large and therefore require additional structural support to maintain integrity. In other words, this line varies slightly from the next lower line in only the addition of some additional structural support. Therefore, if you are looking for a single window to fulfill your width specification, this would be the series/type that fulfills that one wide window type.

There are other quality manufacturers that design oversized windows with the structural integrity required for these large openings. Marvin is a good manufacturer, as are companies like Eagle and you might also look at Kolbe. I am least familiar with the currect Kolbe double hung product, but they revamped their other product lines recently, and did a wonderful job. I think the Eagle line is named "Monumental".

Absolutely go with a double hung window - the light that comes through them are amazing. We‘ve had ours for over 10 years and it’s still holding up strong.