Perks

In general
Every 20 levels, you will earn a perk that gives you either a profit bonus, or a time reduction for your skills.

The pattern is 1 time speed bonus, 3 times profit bonus:


 * 20 Speed


 * 40 Profit


 * 60 Profit


 * 80 Profit


 * 100 Speed etc.

Exceptions
The one exception is strength, which gives: 1 time speed, 3 times profit, and then continues with 2 times speed, 3 times profit.