For me the quickest killers have often been rounds dismissed.. 243 win. 257 wtby has been fairly quick too. I've shot a lot with 06. Never shot with a 270 as I dont' like that round because I didn't agree with OConnor at all.
But bottom line, any round that leaves 2 holes in a deer is leaving behind its energy in the dirt to an extent. A 308 starts with a wider diameter bullet and will still leave 2 holes.
As noted before, I"m firmly convinced speed is a big thing in inducing shock. As are frangible ballistic tip type bullets. I don't like to loose meat and I never shoot high or for bones except the head, and as such the majority of deer I shoot run a ways. Less than 100 and mostly less than 50 steps. Not a big deal to find even in South Texas type brush with a flashlight.
BUT anyone is welcome to use what works best for them. Except me, if I really want DRT, its shot placement over caliber that is the only thing that works 100% of the time.
Interesting anecdote... I started with a 243 Win as a youth around 4th grade. I hunted with that gun for probably at least 10 plus years before I bought a 300 wtby for larger game. Shot a lot of deer with it. The 243 hands down gave more bang flops with lung shots than the 300 did. The 300 gave only one and that was a frontal shot taht flipped a buck over. (not counting head shots on purpose)
Only round I've ever heard of that gave all bang flops was teh 220 swift and it never left an exit. I've never tried it... but that was the rumor from an older local guy that was a gun nut. His family swore he was both nuts to use it and right, it was like a lazer.
