Quoted from yaksplat:Don't half ass it with oak, full ass it with Ipe.
Ipe is 3x as hard as Oak. It takes 3684# to push a .44" ball half way in, compared to 1290 For oak. Birch is 1260# in case you were wondering. So it's pretty close to oak.
I'd so go for slate. For pool tables there are 2 kinds, slate and crap. The slate will not warp or dent ever, it just weighs a ton.