I have one of each of the WSSM chamberings. The accuracy of each of them has been very good. I have spent more time in load development with the .243 WSSM than the .223 and .25 WSSM combined, but the .25 is quite easy to load for and I've takein some fine big-game with it, as well as some long-range varmints.
The .243 WSSM is a little on the fickle side for load development. I have been able to acheive excellent accuracy, velocity and SD with bullet weights from 70 grain up to 90 grain. My use for the .243 never involved the need for a bullet heavier than the 90 grain bullet, so I just haven't done anything with the heavier bullets. What I basically settled on was an 87 grain Hornaday for long-range varmint/predator and an 85 grain Nosler partition for white tail.
I have only heard of a couple of extraction issues. One involved a chamber with a nasty scar and the other involved a .25 WSSM with a short barrel, slow-burning powder and a heavy bullet. It actually extracted OK, just bent the rims in doing so. Feed and function has been great. I have heard of many people running into trouble resizing the brass and not getting the shoulder set-back far enough. If you put a re-loaded shell in your chamber that is 1/2 thousanth longer than the chamber, and slam the bolt shut, it will stick HARD!
All in all, the .243 and the .25 have been very popular, reliable and accurate.