I will add that the odds of an instant kill(i.e. deer drops in it's tracks) increase with velocity and frangibility of the bullet. The kicker with this is that if you get velocity too high with a real soft bullet, you run the risk of blowing up a bullet and getting inadequate penetration. This can leave a deer in the woods with a horrible - but not fatal wound. Nobody wants that. This is why I use controlled expansion bullets in my hot 25 calibers. I've had good luck with Nosler Partitions which I think may still be the best deer bullet for small calibers. The nose blows off much like a varmint bullet giving a good shock effect while the rear portion(about 60% of the weight) continues to penetrate. Hard to beat that. LAtely I have been trying the Barnes 100 grain TTSX. To date I have shot 3 deer with it. All 3 ran but none beyond about 40yds. Obviously it's not going to have a lot of shock effect since it's a solid copper bullet made to penetrate rather than transfer lots of energy fast. It gives me confidence though if I have to take a raking shot at close range even at the 3,590fps velocity. With rifles, it's always about compromise.
In an attempt to get faster kills I've read of some hunters using Berger target bullets that are very thin jacketed and soft for long range shots because obviously they tend to be accurate, shoot flat AND blow up like varmint bullets when hitting a deer. This is great across huge fields when used on broadside deer where all you have to do is punch through a rib. But still makes me nervous if a less than perfect shot is all you get. Or a big buck comes running by right on top of you! (By the way, I have a couple boxes of Berger 120grVLD bullets set aside to experiment with in my 25-06 and 257Weatherby.)
But for the most part because of the small caliber and high velocity of these rifles, I'll hunt with controlled expansion bullets and just accept the fact that about half of the deer I shoot are going to run about 50 yds.