Well,
Nogrod, I understand what you mean now, and I guess we're going to have to agree to disagree on this issue.
I will say that my own impression of Boromir leads me to think that his saving the hobbits is not out of character– which I guess is what you mean by "believability". As far as I can work out, what you're saying here is that since (in your view) Boromir's wanting to take the Ring is highly logical, all his actions should be logical also. He seems to me more of an impulsive type. After all, he didn't just play down the dangers of the Ring, he basically chose to ignore them.
I just don't think Boromir was written as a ruthlessly brilliant strategist, who would always make the smartest, most expedient choice rather than the "moral" one, or anything like that. I think you might be reading things into the character that aren't really there.
And no, I don't want a row either... but you know, this is all reminding me weirdly of
Urwen's "Lalaith".