Good post;Sqeeze is right.
How much velocity any of these cartridges give over the other depends entirely on how hard you're willing to run them.I've toyed with 3 270 WSM's and the factory 130 gr stuff gave a shade under 3300 fps with factory 130 gr loads.With handloads,and RL22,I stopped at 3225-3250.The rifles were a pair of M70 FW's and a Kimber Montana.
OTOH,a custom 270 Weatherby I had built with a 25" Lilja gave over 3400 with the 130 gr Weatherby factory ammo.My handloads operated at about 3350.
I don't own any of these any more mostly because none of them did anything I couldn't get done with a 7 RM and equal bullets.Actually you can take the 270WSM,7mmWSM,7RM,270 and 7mmWeatherby and drop them all in the same hat;there is no difference between them in drop,energy at close and long range,and performance on game.All will go faster than a 270 Winchester because they hold more powder.
Any of them will shade a 270 Winchester in trajectory to 400-500 yards by about 4-6 inches.If your rifle is not accurate,you may not see a difference at all.
The 300 WSM's I've played with (3 Model 70's and a Kimber Classic)were so close to the 300H&H that it was hard to tell the difference.Using RL22,both gave about 3150 with a 165 gr bullet,and right at 3000 with a 180(or so close you could not tell the difference).What one will do the other will do.
WSM brass is pretty tough stuff,and the factories load them to pretty high pressures.
