Should I invest post tax in my 401k?

I'm 28 I currently am putting 13% pre-tax and 3% post-tax, is this a good idea? I make almost $40,000 a year, and can afford to pay the taxes. Will this help me out in the long run? or should I change to 16% or more pre-tax? Also I have 11.23% intrest year to date, is that good, avarage or poor for this year?