Barrel length

[kiwi shooter]

In sure it’s been asked before
But what’s the best barrel length
For a 6.5 Grendel hunting rifle

I want it as short as possible while making sure that I still get good Velocity
Dose dose anyone know the point at which Velocity’s start dropping Exponentially per inch of barrel removed? Ie benefits of a shorter barrel being outweighed by Velocity loss

In my country I can go as short as I want as long as the over all lenth of the rifle from muzzle to recoil pad is above 762mm (30 inches)

The rifle will be suppressed

Thanks in advance