I've ran a game up to level 19.
Levelling is MUCH faster from 11-16. Easily noticeable. Slows down after that though.
Thanks.
I think that while I wouldn't DECREASE xp awards after the PC hit 11th, so they will definitely progress faster to 12th & 13th, after 10th I'll aim to be fairly conservative in terms of non-combat XP, plus I may look to be using mostly groups of lower CR foes with only occasional 'party level plus' types, so that the rate of advancement does not increase too much. I have a lot of material for this campaign (Shattered Star + Rise of the Runelords) and I'd like to use most of it before the PCs reach 20th though I am happy enough to run 'Book 6' of both APs at 20th level if necessary.