IMHO speed is a factor in a kill, but having shot quite a few with the vaunted 257 wtby and 100 ttsx at fairly max loads, I've yet to see one fall over DRT.
Rare for them to go more than 20-30 steps, but they do. Same with my buddies experiences when we bought twins...
And I've had to trail some over 100 yards a few times. A few times with almost no blood.
But they are dead and you do find them.
I have the same results from my 32-20. And about everything in between.
Ran a 243 for years, had some DRT shots not related to shot placement there at times too, then bought into all of hte wtby hype and bought a 300... only deer to ever DRT was a facing shot, 180 partition stopped in hindquarter... so all energy expended there...
Mind you I dont' shoot bones, only ribs and lungs typically. If I want less tracking or meat waste I shoot heads.
IMHO the only way to be sure of DRT is to break up the CNS in some form or fashion, by luck ( high shoulder shooters IMHO) or on purpose.
I do think that there may be a slight edge to faster rounds on the non DRT hits overall, but there are so many otehr factors involved that I"ve seen over the years it almost all goes out the door.
How loud is the shot. How calm or agitated the deer is. Is it rut. Are you hunting a feeder or natural trail, blind or no blind? Did the deer just exhale or inhale? Did you hit an artery or a vein.
Just like blood trails or lack of have various reasons.
As to longer shots, you have hit em right first, wind drift is the big unknown so I have always strived to CYA as best I can on that, and thats not a light bullet typically.... after that bullet construction and speed finally...
YMMV.
