So basically your (or all) electric dryers boil the water out. Remember latent heat of evaporation will significantly reduce your observed temps after it hits the fabric. I'll go so far as to suggest the air inlet temp of that electric dryer is several hundred degrees. The average dryer generates between 10,000 to 20,000 btu. Seems like a little math could get you the proper cfm requirements at the temperature you have available; which is probably a LOT.
The heating element section on the inlet - that thing looks restrictive, does it turn into a 4" round duct as it enters the drum?
I propose a 6" inlet and outlet would do wonders for the drying time.
I like what you've done there. Personally, 1.5 hours would be fine with me for the few cents it costs to run the fan motors, the woman though, huh, well you know how that goes...