I have 35 spline Strange axles in my Fairmont, they have been in since 2000, the year I went from a C6 to the current Jerico 4 speed setup. Never any issues. From 1988 thru 1999, I had 33 spline Strange axles, used with a transbraked C6, I upgraded the rearend when I was making the switch to the 4 speed, as the 33 splines had a slight twist to them.
When I built my 85 Mustang 302 stick for NHRA Stock Eliminator, over 15 years ago, I went with 31 spline Moser spool and axles for the 8.8, as I got a great deal on them. The Stocker engine only ran 12.3s, so not much abuse to the axles, but the last several years I ran the car was with a decent 331 SB Ford, that ran mid-low 10s (best of 10.28 ET), still with a Jerico 4 speed, and the 31 spline axles are still OK. Granted the Mustang was fairly light, about 3000 with me in it, and did not have the torque of a FE.