Bullet choice is the issue with the 270 flavored WSM, much like the 325. I rebarreled my 270 WSM to 7-300 WSM to get the 7mm bullet selection and maintain the 270/300/325 WSM brass selection without having to fireform for the longer shoulder on the 7WSM.
For longer range I'd highly recommend the 7-300 WSM or 7WSM over the 270 due to the bullet choices and the slightly bigger bore will give slightly longer barrel life although it's probalby negligable.
The potential is definitely there with the 270 WSM with the right bullet, but unfortunately there's 2 issues. First about the only redily available bullet that really gets it done is the berger VLD, which is "typically" sensitive to seating depth. Then combine that with the fact that most off the shelf reamers have a LONG throat for the WSM's and you start to run into issues tuning them especially if you want mag fed from a short action.
So if you go 270, make sure it's throated short enough to utilize the VLD's well and maintain your mag (if applicable).
This is where the bullet selection of the 7mm comes into play a lot more than just BC. Mine is a Browning A-bolt, so short action, fairly short mag, and a long throat (had I known ahead of time that reamer was that long in the throat, I'd have ordered a custom reamer) But by virtue of the bullet selection available with the 7mm I've been able to find both match bullets and hunting bullets that shoot great in it. If I were limited to VLD's I'd be screwed because despite trying every seating depth I could, I can't get them to shoot well and fit the mag.
Mine is pretty much strictly a hunting rifle that may see a match here and there (local small stuff) but if I were going to build a custom rifle from the ground up on a WSM, I'd definitely use a long action, to take advantage of all that case capacity, feed it from a mag, and really ring out everything it has to offer.
Just some things to think about when piecing it together, The round (WSM - you pick the flavor) will definitely perform even sacrificing case capacity to fit a short action mag, but in that case I'd most definitely make sure the throating is more appropriate for that configuration before the build.