Now that is the coolest British thing yet! I really like them. Almost has me wishing I had a Vickers over a MG08. You need to get some good video of these guys shooting. If you could team up with Ian at forgotten weapons... it would be awesome to see these guns working today with the history and a modern replication of WWI use. Can you get a big balloon of hydrogen? I would love to see what you can do with this.
As far as them hitting harder... I wonder how it will compare.
30-06 = 2,429 ft⋅lbf
303 = 2,408 ft⋅lbf
45-70-405=1,748 ft⋅lbf
45-70-300=2,852 ft⋅lbf
So it looks like it depends on exactly what 45-70 you are loading up. I would be interested to know if you can feel the difference when shooting the gun.