I'm not 100% sure on this either, but I think the damage formula works like this.

your base damage * (1 + percentage damage bonus from int) * (1 + percentage damage bonus from skills) * (1 + percentage damage bonus from height)

and 60 int is basically 50 bonus int x 5%, ends up with 250% inc damage, plus the base, 350%.

6 rank in a skill is 6 x 5%, 30% bonus, plus the base damage, 130%.