Enh should gem AP or Haste?

My Enh shammy is nos bis geared I have 5200GS I've already got hit and exp cap without needing to gem it I see a lot of high GS Enh and different gems some people gem only haste on all sockets others gem only AP and I've seen some ap+haste gems, so I need some help in what stat will be a better choice for me I'm currently running full haste gems but would ap be a better option?

Melee Hit cap depends on your crit chance. When you are better geared you'll need additional hit to extend your melee crit cap.
You should use hit or haste gems for yellow and hit/exp or exp for red.
AP gems shouldn't be used at all.

would you mind going into a bit more detail about that hit-rate/crit-cap relation there?
at what point would you need to raise hit above the default melee hit-cap?
is that something i gotta worry about already going by how my enhancer is at a lil over 40% crit unbuffed
and at what ratio would the hit rate have to be increased etc.

thanks in advance