Meta Gem
Insightful Earthsiege Diamond is the best. It isn't even an argument in both theorycraft and real raid application has been shown to be the King.
Seriously, put down the 2% to intellect one. Both in theorycraft and also in actual encounters (via WWS) it has been shown that its not even a close race. Insightful wins by a mile. Putting in the 2% intellect one is like a Hunter gemming for Strength, ok maybe not that bad but you get the point.
SP
Don't gem for it. Stacking SP is bad for a holy paladin, unless all you do is spam FoL. Which if at lvl 80 you are still spammng FoL you need to get sat down. All it mainly does is contribute to overhealing. You will have to have 1 gem with it for the meta but honestly leave off, with current itemization you are good for Spellpower quit measuring your ***** by it. Its not healthy.
Mp5
Don't do it, honestly mp5 is trivialized for pallies.
Int or Crit or whatever floats your boats, honestly I don't mind a little variation but bad meta is bad, gemming entirely for sp is bad and gemming Mp5 is terrible. Stop it.