4 key is about the most I've ever really needed. I have done 5 once before, but that was more because I wanted to do something different (basically, had a global hotkey setup to lock my desktop if I hit control-shift-winkey-alt-z or basically mashing the lower corner of the keyboard).
A handful of games will hit 4 or 5. if I am doing a spiraled climb while targeting and firing at missles in BSGO, then I hit limits sometimes.