Mike375,
Both cartridges have about the same body diameter which would be concidered the 'piston' diameter. The 300 Wby would probably reach peak pressure faster than the 458 Lott but drop of sooner because of bullet speed. The 458 Lott would take longer to reach peak pressure and drop off later because of bullet speed. So, in my oppinion the bolt thrust would be about the same with about the same duration for both calibers.
Headache

Your thinking is muddled. Pressure is pressure and the only pressure that matters is PEAK.