Ireland has a massive amount of talent, a lot of creativity, good movement and is a major threat going forward.
Milner is a totally different player, he's far more hard working and is pretty good at everything.
If we do sign Ireland, i do feel we'd need to sign a different defensive midfielder with a lot more about them then Petrov in terms of energy and defensive ability. Whilst i really like Petrov, if we're to lose Milners drive, it needs to be replaced somewhere.
Bottom line is, Ireland will give us much more creativity going forward, and if we can cover defensively in what we'd lose from Milner, then... i think we'd be alright.