I saw a heavy increase in my heals when I dropped all of my mastery gems for int gems.
My armory:
http://us.battle.net/wow/en/characte...ashwa/advanced
I went from 43% mastery buffed to 37.5% mastery buffed, but I gained 2k int while doing it. My healing felt much better, much stronger overall. After all, Intellect will triple dip. 1) it gives you a stronger hitting spell 2) since the spell is healing for more, you'll get a bigger shield. afterall, if you heal for 100k at 43% mastery you get a 43k shield. If you heal a 120k at 37.5% mastery you get a 45k shield. 3) more int=more crits which will equal even bigger mastery shields.
Summary: I saw a big improvement in performance when i regemmed int.