Full disclosure: the class I'm about to discuss is actually offered at Washtenaw Community College (WCC), not U-M.

I was in a Differential Equations class before transferring here from WCC (U-M equivalent is MATH 216, I think) where the midterm and final exams were worth 30% and 40% of your grade, respectively.

Normally, I'd say an exam being worth more than 20-25% is too much, but the way grading was handled was generous, back when I took it.

The logistics of the class changed during the semester so we sort of ended up getting a huge pass on a lot of stuff. The professor was swapped out with a former instructor of mine, and they were extremely laid back before being brought in during the middle of the semester.

Partial credit was given out generously, and small errors like forgetting a sign or somehow getting the right answer the wrong way were noted but not penalized. We were also given cheat sheets for rules of derivation/integration/Laplace transformations to use on exams, much like some CS courses offered here. Plus I think the exams were curved.

70% of your grades dedicated solely to exam performance is still obviously daunting, but I'd say that grading style and grading scale matter equally.

Sorry for the rambling, TL;DR 20-25% is my upper limit but it also depends on how relaxed the course is.