The Lott has a larger case than the WM. All things being equal, it will give 50to 70 fps more than the .458WM. Stories about 200 fps faster are a myth. Maximum velocities in each require compressed loads (see Barnes Reloading Manual #4). High pressure in the .458 or in the Lott is a myth with modern powders. It stems in part from the temperature sensitivity of obsolete cordite powder 100 years ago and in part from some problems that Winchester had with WW748 ball powder in the 1950s. It is simple to get 2200 fps with a 500 grain Barnes banded solid in the .458 WM but WW 748 is not a very good powder for attempting this. Winchester uses WW748 because they make it and they're too cheap to buy some good powder. That's why their velocities are lower.