Been watching this thread for a while.
To the OP's original question, yes, speed matters.
I build all of my LR hunting and comp rifles with a velocity 'window' in mind for a maximum range.
Recently, after trying a 338 Edge, I discovered it still fell short of my minimum 3000fps with a 300g pill.
I am now basing all of my builds around the Rigby/Lapua/XC cases.
My own designed 338-416 Rigby Improved 45° shoulder does what I require, but the brass is lacking in strength when I use Norma brass. Hornady brass holds up, but is inconsistent in volume across the batches I have bought.
TOF matters in the wind, which is why, for me, old school cartridges that are fast for calibre are what I use in F-class, 300WM predominantly, but I also use a 264WM, 6.5x47 and a 22-250AI depending on conditions and range, the latter 2 only get used in good conditions and only up to 600. TOF at those distances aren't as critical, but the 77g pills I use in 22 cal still get moved around by the wind, even a slight breeze.
For hunting, it's the bullet you choose that is the limiting factor as far as I'm concerned for what speed and range it's going to work at, if it's above or below it's 'best' performance window, then you need to adjust for that.
Lately, after some extensive testing, I really like the low velocity performance of the Nosler ABLR, have used them in 27, 28, 30 & 33 to date at 1300 and they still expand even when only doing 1100-900fps.
I have had issues with certain Berger pills not performing at these velocities, hence why they were not performing outside their 'best' performance window.
Anyway, paper and animals are vastly different and need careful consideration when choosing pill, speed and range.
Cheers.