Considering the amount of powder the 300 Win Mag can swallow up and that powder usually being slow or slower burning, a barrel in the 26"+ or more range might be a good idea.
Seriously doubt you are going to shoot a 'Rattle Battle' string with a 300 Win Mag, or for that matter a 200 yd. or 300 yd. rapid fire string which is 10 shots in 60 seconds and 10 shots in 70 seconds respectively. With that in mind you would have little need for a straight taper and or an MTU taper and Sendero probably should work for you.