No, I haven't seen actual tests, but I know when one of my friends changed from an 18' box-shaped TT to a 25' Avion he was surprised at how much better it towed!
I would suspect that a
Casita 16' would tow better than a
Casita 17' because of front profile area and shape.
Underside drag in front of trailer (not lined up with TV), aka air dam, can make a lot of difference also. I found that out when I did a spring-over and put larger wheels on a Jayco.