What is the numerical advantage of each added inch of draw length in Feet per second.

Like a for instance:

I am drawing 55 lbs.
I am shooting a arrow at 8.6 gpi with a lenght of 29 inches& 100 gr. BH
My draw length is 29 inches

Then say I make my draw length 30 inches.
What does that extra inch gain me in fps?

Justeven a rough estimate would suffice. Not trying to melt the calculator or anything like that.

Thanks