What if Boromir had taken the ring?

[Gwaihir the Windlord]

I remember reading this one somewhere:

ALTERNATE ENDINGS TO LORD OF THE RINGS
'- Boromir takes the Ring, travels back to Minas Tirith, defeast the armies of the Dark Lord and becomes a wise and benevolent ruler. Book ends 38 chapters shorter...'

Although I agree that was impossible. I don't think Boromir would become like Gollum; because of his greater strength of mind, valour and opposition to Sauron, he would try to attack Sauron. That was, after all, why he wanted the Ring in the first place, to save his people. Gollum was just greedy.
Gandalf, Aragorn etc. would have no chance to stop him. He would just slip away into the trees... although it is possible that in Minas Tirith, Denethor or Prince Imrahil may take it from him.