You REALLY need to know what "rated load" means for any machine component.
EXAMPLE: a bearing has a dynamic load rating of 100lbs (purely a number for illustration). This does not mean that you can put a 100 lb static load on it and it will run for the projected fatigue lift. Chances are, it will fail in a very short period as "rated load" is NOT what you can load it to but a labratory method of CALCULATING life using a controlled, industry standardized (not necessarily real world) method.
Now, if you start at a 10 lb load on our hypothetical bearing and ramp up to 90 or so, you'ldd see much more life that may or may net match the rated life a bit closer. The explanation is too invovled to go into in a message board. You can find out more by looking up "bearing L10 life calculation" in various bearing handbooks.
The point being made is this: rated load usually means something to the guy who MADE the part and something totally different to the guy who's going to USE the part and it does NOT necessarily relate to real live loading conditions/potential.
Do your research carefully. Run at a lower percentage of the rated load for anything and you'll see much better fatibue life. Otherwise, be prepared to feed the system parts on a regular and nauseating basis.....