Teampete,
You are wise to decide against adding another grain of powder to an already near max load which is showing possible high pressure signs. I seat loads .010 off the lands of my custom 300 WM, however, (as mentioned before) every rifle is different. What may help you to understand is the 'jump' a bullet is allowed offers the burning powder the chance to build pressure and thereby giving the bullet a 'running start' to take the rifling. If your bullet is jammed or too close to the rifling, it will likely produce a pressure spike. With loads that are not near max, this is typically safe and acceptable, but with a near max load to begin with, you are adding to the pressure with this spike and risking dangerous pressure levels. I would suggest either lowering your powder charge and play with your seating to the lands (this would lower your MV, but most likely improve accuracy) or keep the max load and seat the bullet deeper to eliminate the pressure spike (this would take a little away from accuracy, but offer higher velocity).
Keep in mind, magnum cartridges tend to burn barrels with hotter loads, which is why I tend to reduce my loads for the time being. Considering you are using heavy projectiles, they will go much farther than your lower weight bullets anyway.
In addition, many primers do flatten (slightly) in magnum cartridges. This was a concern I had when I first began reloading for my 300, then I found out it is usually normal and not necessarily an indication of high pressure.
Good luck and be careful.