First of all where did you get the info that crits do 50% extra damage? It is in fact 100%.
Thus your little example goes out of the window.
Second of all you have to take into account two things:
- how ratings convert to percentages
- how much stats you already have
For level 20 arcane mage rating to % conversion looks like this
- 1 crit rating = 0,29% crit
- 1 haste rating = 0,31% haste
- 1 versatility = 0,25% more damage
My blood elf lvl 20 arcane mage has following stats:
- 174 int
- 20.19% crit
- 4.6% haste
- 4.91% more dmg from versatility
I use following formula to estimate dps gain:
Int * (1 + Crit%) * (1 + Haste%) * (1 + VersDmg%)
Dps increase for each additional point looks like this:
- 1 int gives 0.57% more damage
- 1 crit rating gives 0.24% more damage
- 1 haste rating gives 0.29% more damage
- 1 versatility rating gives 0.23% more damage