The SAAMI limit is 40,000 psi compared to 36,000 psi for the .44 Magnum. Not a huge increase.
The .445 is a handloaders cartridge and a handloader does not need to load to the full max pressure. Even if one were limited to a maximum pressure of 36,000 psi the larger .445 case would generate about 200 fps more at the same pressure as the .44 Magnum.