It would be dificult for me to say exactly since I have not shot the 270 Short magnum. Logic would dictate with the variables being the same: rifle and bullet weight, I use 48-50 grains of powder with the various bullets in the 6.5. How much powder is used in the 270 WSM? Logic dictates more, therefore there should be more recoil.
I have owned both and my scientific evaluation is that the 270 wsm kicks "a lot more." However, the wsm is still not unmanageable. I have shot 20-30 shots in one sitting with the 6.5-284, but I wouldn't want to do that with my wsm.