the Barnes perform best above 2000 fps so run them as fast as you want.
Yes the rigby can be loaded almost equal to the weatherby. It's up to you what you decide is a good balance of velocity vs recoil. If you load to 416 remington specs you can use a ton of different powders to get there.
I'm using the remington version of 416 so I don't have any loads, but you should be able to get all the performance you want with lower pressures in the rigby.
