Determening casting speedFollow

This might be a subject that have been trampled to death already, but I still want to give a go at it.

Info below might be / might not be fact, but it's info that I have picked up around, and when combined might give some interesting info.

Note what I'm looking for is how to determine how much DEX you need / should have given some background information.

1) Hard casting cap of 2.0s
2) Max DEX % bonus is 25%
3) DEX casing bonus is 1% / 10 level til 250, and 1% / 20 level over
4) ToA bonus to casting speed max 10%
5) ToA bonus can override casting speed cap

Now, given 2 & 3, I can't see a reason to go with more than 250 DEX total. Given I'm always buffed, I could now use any excessive DEX for other stat/resists instead?

Casting bonus speed I will assume is subtracted from base casting speed, so with a PBAOE of 2.5s, 25% will be 0.62s, and result in 1.875s, which is less than casting cap of 2.0s, so 20% is all I can utilize, or in other words DEX 200 is my 'cap' in real life.

As you (and I) can easily see there are some obvious 'wrong' to this, as if 1) 25% is max casting bonus, why do they list what bonus you get after 250 DEX ? (250 / 10 = 25%).

So I was hoping that somebody who have tested this out / found the answer could enlighten me on this issue ;-)

- Gnabgib / L50 RC [314 DEX]