Wow, I'm out all weekend for my daughter's 7th birthday weekend, and look what happens!
Okay, I'll clarify what I said and give my thoughts. First off, Hunter got my statement correct, albeit without the surrounding context. The facts are the facts - best I can gather from talking to a lot of people who own both 7mm & 270Wby's, and from shooting a lot of rounds over my own chronograph from my 270Wby - the 270Wby is about 50-100fps faster than the 7mmWby with equal weight bullets. In fact, it's a couple hundred fps faster with comparable weight for caliber in some instances, as I can safely get 3500fps out of 130gr bullets in my 270Wby and they compare in SD and BC to 140gr bullets in the 7 which will run about 3300fps at best from what I can gather. So, the facts show that the 270Wby is faster with equal weight for caliber bullets, as I've said many times. I'll step further out on the limb and add that it is also marginally faster with equal weight bullets, which is a bit bigger deal, as the higher BC and SD of a 140gr .277 bullet can be significant in longer range field situations (400-500yds).
Now, the only reason I can come up with for this is that the bullet weight, caliber, and case capacity hit some sweet spot right around the 130-150gr 270Wby loads. Or, perhaps it is such that pressures are higher in these rounds, but I doubt it based on the consistency across a number of rifles and both factory loads and handloads.
In the real world, there just isn't anything I'd carry a 7mmWby for that I'd feel undergunned with the 270Wby, and I get anywhere from 10-20yds more point blank range with the 270Wby than is workable with the 7mmWby. I realize 10-30yds isn't much difference in point blank range, but it does also equate to some significant differences of half to a full minute of angle at 400-600yds. Let's remember that at those distances, half a minute of angle is 2-3" difference in trajectory, which could mean the difference between a lethal hit and a wounding shot.
Now, if you own a 7mmWby, don't fret. For just a little bit of money you can acquire a 270Wby in a nice Mark V, and be on your way to rifle nirvana.