by decent championship player I mean that is his absolute ceiling. His potential is between 90-120. 120 is a decent championship player. 90 is a League 2 level player. So chances are he will be somewhere between there...
But that's if he reaches his full potential. Which he probably would do if at a decent club with decent facilities, but at a club without decent facilities there's a good chance he wont.
None of this changes the fact that he should be signed anyway. Just making it clear so he doesn't let you down