I am a gunsmith and I have made, sold, seen used, and used the 25-06 for almost 40 years. It's one of the best deer calibers made. The only caution I'll give in hunting deer with it is simply to NOT use bullets that are too thinly jacketed.
The 25-06 is a bit over bore and very very fast. It's not called a "Magnum" but from the standpoint of a cartridge engineer, it absolutely is a magnum.
It requites good bullets to work to its potential. Avoid bullets of any weight that do not hold together on impact. Just because a bullet is 120 grains is not a guarantee that it’s going to stand up to the impact at 200 yards of closer.
I have friends that I was hunting with Waaaaaaaay back when I was a very young teenager who used 25-06, and I also have guided hunters now for over 40 years, and I have seen them used on big western Mule deer, Whitetails, and some on black bear and even elk.
Many .257” bullets have been in production since the 2 most popular 25s were the 250 Savage and the 257 Roberts. They have not beefed those bullets up in 60 years. They are fine for shells that throw them at slower speeds, but just are not up to the task of a close range shot on a deer at 25-06 velocity. Sure…..they will kill, but they often don’t penetrate as well as we’d like and the meat destruction is awful.
I own a 25-06 I made for a very dear friend of mine, Bob Ellis. I made 14 rifles for Bob over the years I knew him, and he was a fineman, a true friend and game shot the likes of which most men only dream about being. He died a few years ago and he left it to me. Bob was a real rifleman and I made rifles for him from 223s to 338s. The one he liked most at the end years of his life was the 25-06.
He got too old to go after elk, but was a deer and antelope hunter right to the end. He left me his favorite rifle when he died and I treat it as an old friend would have wanted me to. I hunt with it now and then, and I know what it’s capable of. Bob used that rifle to kill about 10 head of game when I was hunting with him, and i have killed 8 deer and antelope myself with it.
The bullets I have used, and seen used that make the 25-06 all it can be are the Nosler Partitions, Barnes X and Triple shocks, 120 grain Remington Core-Lockts, Swift, and all the new bonded core bullets.
For varmints (nd anything you don’t want to keep the fur from,)the 100 grain Remington is good, but they will blow up in a coyote. In Bob’s old rifle and in most other 25-06s I have tried them in, they hold under MOA, but they will not hold together on a deer. If you want to kill varmints however, they are cheap, accurate and will cut a small coyote or fox almost in half.
Ok….I have rambled on long enough.
I hope this help you, and happy hunting.