Minecraft documents Fortune here: Fortune – Minecraft Wiki
According to that math, Fortune 3 is 1/(3+2) + (3+1)/2 = 2.2x ore.
Then Fortune 5 is 1/(5+2) + (5+1)/2 = 3.14x ore.
To summarize, boomsticks give roughly 2x the ore and dynamite give roughly 3x the ore before doubling in the crusher.