Ren
i don't know how much lower, but the rule of thumb for going BIGGER is you will gain velocity at the rate of 1/4 of the percentage gain in capacity, at the same pressure. Do the math backwards, and its very intriging.

i don't care for plated brass, and only use norma for 45/120, due to construction and capacity

you are welcome to your 45/70, I have a couple. However, THIS build is about the 45/120 on MY huglu ... i wouldn't have bothered with the work, as my spartan does 45/70 work just fine