There is a practical length that you reach with any barrel, (Velocity, Accuracy, and manageability.
That being said, there is a point of diminishing returns. After an optimum length is reached (The length that the velocity per/inch of barrel starts to decrease adding more inches does not add much velocity and at some point depending on the barrel contour may/can start effecting accuracy due to the harmonics.
The 270 wsm can certainly use a 28" barrel and benefit some from a 30". beyond that the increases in velocity will taper off.
The main advantage you will see is when shooting heavy bullets. the longer barrel will allow the slower powder to completely burn as long as you use the right primer.
As far as accuracy Shorter barrels are normally more accurate because the harmonics are better and the barrel is stiff. The longer barrels have more whip unless they are the heavy tapers, contours.
Dan Lilja did a test on maximum barrel length and started with a 46" barrel and cut 2'' inches off
between each test.
Lilja Precision Rifle Barrels - Articles: Barrel Lenghts and Velocities in the 338/378 Weatherby Magnum
Hope this helped
J E CUSTOM