Gnat driving, is any rifle that can hit tiny tiny gnat sized targets. Gnat often used in marksmanship training where an imaginary gnat is placed on a target; shoot at the gnat, not the animal.
Farmyard ranges are anything below 25m or 25yards, what you might find hunting around farm buildings and surrounding areas. Basically not very far, and most even able with iron sights.
Beyond 25m then the kit and marksmanship level really is exponential in difficulty.
Anyhow, the range is dependent on the conditions of the day, though at Farmyard ranges conditions aren't as dramatic. Further then even the mildest of wind has to be factored in.

Beyond 15m then:
Hydraulic shock at these energies really is minimal, miniscule. It cannot be relied on to correct any shot placement error.
Energy transfer isn't of a dramatic enough level either, and all the larger critters taken on can shrug off such energy.
The only thing that matters is the "slightly enlarged" stiletto wound tract through a vital. That the tract passes straight through or not makes little difference in instant results. A .177 is massive damage to a small brain or heart that normal air gun quarry has.
Why only shot placement through a vital matters.

Projectiles with more energy then everything changes.

Again, how easy is it to find a .20 ammo that delivers exceptional accuracy from any barrel? As I said you might be lucky, or not. There isn't the choice of ammo to try as with other calibres.

Buy one, have fun with one, but don't pretend "it's better".