I'd agree, accepting 1/14 if that was all I could get in a blank, but no slower.

As for length, my opinion is that it 100% depends on the use of the gun.

For instance, I would jump at an 17 or 18 inch barreled carbine in .35 Whelen for following bear hounds or as a saddle gun, but also could find a lot of practical use for a 24 or even 25 inch barrelled rifle for general deer and elk hunting.

What would it be used most likely for?