Basically just echoing sentiments here, but I only use 4-man rotations because I prefer the extra bat/pair of legs on the bench. I agree with rdierkers in terms of pitch count - I set my 4 starters at stamina+10 for target and stamina+20 for max. If a guy is 30+ durability, I up his max to stamina+25.
Add 2 guys you're comfortable picking up that 5th start (in case one is fatigued from bullpen duty) and have at least 1 guy (usually it's a mopup guy for me) that's just an innings eating machine when needed - 40 STA, 60+ DUR.
I've had good success with this strategy and have only gotten into fatigue trouble due to multiple, consecutive extra innings games or freak injuries.