To many speed freaks out here. Speed is needed to get a projectile to its target in a hurry, especially on DG.
But the 2 most important factors:
1. Bullet performance.
Bullet manufacturers are designing bullets to properly function at specific thresholds. THEORETICALLY as long as the bullet is within these thresholds the bullet will perform properly and do its job. It's of course the shooter does their job on placing that bullet in the kill zone.
2. PUNCH!!
If the bullet fails to penetrate or deliver enough energy to knock the target down the shooter needs to rethink and increase his/her choices.
There are 2 methods/ideas/concepts/ whatever ones choice in describing:
Velocity: by which shock can adequately or inadequately humanely kill.
Punch: energy to actually kill.
Personally I prefer punch to velocity. I follow the 1.5x rule. Providing the caliber/bullet I select has a knock down factor of 1.5 x the weight of the animal I intend to kill, all is is good, it's up to me to place the bullet in the zone.
Others believe the faster the bullet the better.
Dead is Dead!!
Does it really matter how close or how far the hunter was?
Does it matter how much or how little the weapon cost?
Does it matter how fast or how slow the projectile was traveling?
Does it matter how beautiful or ugly the weapon is that sent that projectile?
The answer is: NO!!
I frequently use the analogy between a Ferrari and a Mack truck hitting a concrete wall.
A Ferrari traveling at 160 mph hits a brick wall pretty much disintegrates the Ferrari yet the Ferrari does penetrate to some extent and past the wall.
A Mack truck hits the wall at 80 mph not only damages the truck, the mass and heavier weight of the truck allows the truck to travel further past the wall.
The sleek Farrari looses most of its energy on impact. The bulkier truck spreads its energy over a wider area allowing more of its energy to penetrate and push past the wall.
Apples to apples--Oranges to oranges
ONE CALIBER: and NOT comparing one caliber against another.
Also, not every firearm from the same manufacturer is as accurate with the same load, some may require a higher velocity with a lighter bullet, some may require a slower velocity with a heavier bullet.
Load your rifle with the combination that it likes and that you can shoot with consistent accuracy, you will be fine.
As for using a single shot hunting DG, check with your PH. Especially if other DG animals are in the area.
Just my 2 pennies.