I learned that when you improve one part the next failure will be down the line somewhere.
I built performance 1600 class VW engines. Then I learned how to beef up the transaxle, the next thing in line were the axles and rear brake drums. To improve the axles would of cost too much but I had a ready supply of them along with brake drums. So I never went to better parts.
My nephew found out the expensive way. He had one of my engines and transaxles in his VW, and thought that he had blown a clutch so he replaced it. He still couldn't get it to move so I went over to figure it out. It turned out that the rear disk brake rotar that he had put on has all the gear teeth sheared off on both wheels, so the axles just spun inside them.