It depends ...
As i understands it, leveling fast first few levels is one of signature things for DnD ... many classes choose their sub-class on level 3 and it would really suck that they would need to wait for it til middle of Act1. :-/

Also concidering this:
[Linked Image from i.imgur.com]

Doing level 5 would take aproximately 1,5x as much time as all previous levels together. O_o
Same with level 6 ...
And im once again too lazy to count the others, but i gues it will more like slow down, than rush.

I still dont understand why cant we change Race for our hirelings. frown
Lets us play Githyanki as racist as they trully are! frown