I know it sounds crazy but when I used Mach 3 carts (years and years), I would use them and never remember how long it had been on the razor and would change it "just because". Then a few years ago I decided to endurance test a Mach 3 and got 75 shaves on one cart but only quit using it because I had become thoroughly bored and wanted to get back to DE. I had started stropping it on denim around shave #30 and though it was beginning to feel rough toward the end, it was still cutting and would have gone on past 75 if I had pushed it.
These were all one-pass shaves with an additional ATG pass on the cheeks and minor neck touchup.
I used to get about 60 shaves with my M3.
Most people on this board were quite surprised at that.
Tugs quite a bit for the last quarter.