Tyler also had trouble with regular formula (Similac Advance). Gassy, fussy, spit up etc. So at 6 months we finally switched him to Isomil which is soy based. Once he turned a year we gave him Lactaid Milk (both DH and I are lactose intolerant).
Once or twice we have given him regular whole milk just to test and he was extremely fussy those days so I do not dare try again.
Not sure if this info helped.....
But I think if Nathan had trouble with regular formula there is a pretty good chance regular milk might give him trouble too.