Durable, powerful window fan?

Our fleet of four Honeywell-brand window fans (similar to this) finally had to go to the curb this summer as they'd developed an uncleanable case of mold and mildew and the plastic was starting to degrade. They served us well for 15 years, though, and in almost constant nighttime use through the summer and fall.

We're looking to replace them, and are having difficulty finding something as durable. I picked up a couple of Bionaire window fans last night and tried them overnight, but found them wanting: their air throughput was about 1/2 of what our old fans were capable of, and so our rooms were as warm in the morning as in the daytime, despite cool temperatures outside.

At the same time, the fans we're replacing, in their modern incarnations -- two-fan or "Twindow" fan models, 7" blades, etc. -- seem to have plummeted in build quality and features.

We're looking for something that will last, and that can pull lots of air into our warm bedrooms on cool summer nights.