I had a 25/06 several years ago. It was a good little rifle but I wasn't overly impressed with the time it took deer to fall with it. I believ I was shooting 115gn Federal BTs. And while I haven't owned one yet, I have played with and been around several 257 Wbys. quite extensively. With a stout handload and premium bullets like Barnes X bullets the 257 is a real lightning bolt. I also realize that you can stoke up the 25/06 with equal bullets as well. But as with every other caliber, when you are comparing 30/06 cased variants to 300H&H based variants its the magnums that begin to outpace and shine when you begin shooting heavier bullets in each respective caliber.
When you get over 115grns in a 25/06 it begins to loose some of its luster too the 257. A 200 fps difference is on the threshold of "becoming worthy of consideration" and a 300fps gain is flatout worth a try. Remember that to double a bullets energy you dont have to double the velocity. You only have to increase the velocity by appx 1/3. Being purely hypothetical, if a 100grn bullet fired from a 25/06 @ 3k fps could be increased to 4k fps (a friends Lazzeroni Scramjet gets AWFULLY close!) the energy would be doubled. Now increase that 3fps bullet too 3300 fps. Thats appx a 30% increase in energy. Or if that bullet was producing 2k ft#s of energy @ 3k it would now be producing 2600 ft#s. Thats a credible increase IMHO.
But realistically the 25/06 is a real favorite among guys gunning for deer at long distances without the desire to get a magnum (personally I would rather have a 270 for the same conditions but I like more power than just enough!). Where the 257 pleads its case is when driving heavier bullets plenty fast and when really juiced with premium bullets of 117-120 grains you CAN look at taking larger game with it (again, not my ideal elk round, but tell Roy Weatherby that the many elk he killed with it were just figments of his imagination!).
Whats wrong with having one of each for no more reason than, "farts n giggles"?

RA