One 90 vs two 45s in an air duct. Which is better? 

You really should’ve added a short straight pipe to the 90° turn since the 2 45° turns or a much longer section. That way you’re at least equalizing the friction of the pipe walls between the two data sets.

2 45s even 22.5s get u 15 to 30 percent better flow my expierence v40 yrs plus ground wire over 4 inches

Good job ❤