In this head to head example..with identical bullets, there is no debating that the .243 WSSM is ballistically superior.
Zexpilot...I would never tell anyone to trade in their gun for this difference in ballistics, but head to head, same type and grain of bullet the .243 WSSM shoots flatter.
James B...these are actual factory loadings. The reality is, (at least for this cartridge) the .243 WSSM shoots 150fps faster.
Now the real question....is 150fps at the muzzle and 2in +/_ at 400yrds a big deal. I cant answer that for anyone but myself. But I know if I could get a gun with a stronger action, that weighed less, and was shorter, with the the same barrel length, and shot a given bullet flatter, I would take it.