it doesnt matter if your bottle reg is outputting 450 psi or 850 psi, or whatever, your inline reg on your ion should be set to bring it down to the operating pressure of 170psi, or whatever it is.
Be a bit careful if you go from a LP reg to a HP reg, you will need to dial the inline reg down a bit.
The difference between a 3000 psi bottle and a 4500 psi bottle is just capacity really.
Hope that helps a bit?
Laters - Ste