As a response to 7, 10 was holding it in so he could see all his companions again as himself and could do no longer when he reached the TARDIS. The build up of energy made it explode out of him whereas with 9 he just let it happen.
AWWWWWWWW OMG IM CRYING TEARS OF PERFECTION ASDFGHJKL I LOVE THIS SO MUCH! THIS. I JUST CAN'T. (Sorry to my followers who don't ship Johnlock) I actually am sorry, but not sorry enough to stop pinning Johnlock