flying speed of ranged spells?

[Shokarta]

Hello,

is there a way to calculate (or to know) how fast all ranged spells are flying?
how many yards per second?

Im developing the addon which blocks spells when the target has the debuff.
For example, doesnt make sence to keep casting Serpent Sting when target still has the debuff.

However in order to improve, I wish to have been able to cast again when target still has the debuff but the debuff will fade before I hit the target with the spell.