Have you actually weighed the arrows? How did you arrive at the 4.7057 gr/lb?

Here's what I get.. but it also depends one what components your arrows have.

28" x 7.3gpi = 204.4
insert = 11
nock 13
point 100
vanes 24
Total 352gr

which equates to 5.029 gr/lb... Which is right at the IBO standard. Yes you can go heavier.. but I really wouldn't worry about that too much. I'd be more concerned about the spine being too weak.. With your poundage I'd think you'd want the 350s... which would also bring your total arrow weight up around 400gr or so.