QH, there are several factors in my choosing the Mike Rock 5R 11.27 barrel but the final kicker was an article on shooting the .300 WSM to 1000 yds by Ian M. in Gun World, in May 2002 I believe. Some of the other factors that I remember were my gunsmith's claims of longer barrel life, less stress on the bullet during barrel barrel time resulting in better external and terminal ballistics, potentially higher velocity, and it would be very likely to shoot the 168 XLCBT well.
The same barrel is used on the U.S. Army's M24 7.62 NATO(.308Win) and does extremely well with 175 MKs. I have been told that the few M24s in .300 WinMag are perfect for the A191 cartridge, the 190 MK at 2950 fps.