I've used a 7mm Wby Mag and a 7mm Rem Mag, both are really good. I've made 5 consecutive one shot kills with the 7mm Rem mag. I switched to the sendero barrell in 2006, the accuracy is just too much too ignore. Plus, if you are ever in a bind, it would be much easier to find a box of 7mm Rem Mag ammo.
As far as the .300 Mags are concerned, great guns no doubt. However, I've shot and hunted with a .300 Wby Mag, the extra kick is pretty obvious. If you are a big dude, then it isn't as much a factor. However, for lighter folks, it can rock you pretty good. I think it can have an impact on accuracy. I've never noticed the recoil from the 7mm's.