From the stats I just looked at they look remarkably similar, with Seanez having the edge in K's and IP over the past 3 years, while Borowski appears to be the better save-man. Over the past three years they have almost the exact same BAA (.241 vs. .242), yet Borowski has an ERA that is a run higher.
Nothing definitive, but just some simple stats to look at. I think that, before we had Seanez, it would have been hard to evaluate this proposed acquisition without picking Seanez.
Face it, folks, I think we're bound to have a number of "big name" relievers fail in Fenway. Baez interests me, for sure.