MPFD,
Your comparison of the Rem 7mm mag and the 7mm WSM are correct. You will NOT achieve any performance increase in the way of velocity with the WSM. The same is also true for the 300 WSM.
But, The one I am looking at is the 270 WSM. If you will look on the same website you used you will find the following:
130 Grain Bullet
270 Win:
http://www.nosler.com/index.php?p=15&b=270cal&s=87
270 WSM:
http://www.nosler.com/index.php?p=15&b=270cal&s=99
The WSM is anywhere from 204-375 fps faster depending on which powder you are using. The 160 grain is about the same margin.
There is a greater margin between the 270 Win and the WSM than there is between the 30/06 (which is a great cartridge) and the Rem 7mm mag. Back in the 1980's a whole buch of people went out a bought a 7mm mag because of the extra power (I know because I was one of them). I think it is justified to do the same now with the 270 WSM. I have never shot one, but the online reviews that I have read say that they group as well as the 270 Win. Unless I change my mind, I will be purchasing a 270 WSM sometime next year. But, if I still owned my 7mm mag I would probably not buy a 270 WSM.
I want something that gives a little less recoil than the 7mm and will accept a bullet under 100 grains. This way I will be tempted to use it occasionally through the year when I am coyote hunting (Speer and Sierra both make a 90 gr varmit bullets for the .277 cal). Before, when I owned the 7 mag, the only time I took it out of the gunsafe was a month before deer season. I paid ALL that money for a gun and good scope and shot less than 20 practice rounds per year and shot 2-5 rounds hunting in the field. I want something I will be more inclined to use through out the year. It will not replace my 223 for predators, but give me an alternative.
But let me qualify one thing: I am NOT knocking the 7mm mag. It is accurate and deadly. Since 1986 I have owned 3 7mm mags. I hunted in Calif, NW Colorado and Oregon with it. I killed Mulies, Blactail, and Antelope. Everything I ever shot with it traveled less than 20 yards before piling up. Most never made it that far.
Calcoyote