Also, let's wait and see what actually happens before we declare what "NFL GMs seem to think." Going into the 2008, Brady Quinn was "projected" to be a top-10 or top-15 pick, and slipped to late in the round because, in fact, nobody knows what the GMs think until draft day. Leinhart slipped to lower than expected. So did Geno Smith last year.
But even if he is a top-five pick, that's still no guarantee of success. Rivers, Russell, Young, Alex Smith, Harrington and Sanchez were all top-five picks of those that I mentioned. Only Rivers and Smith had any meaningful success as quarterbacks (and Sanchez played on a team that went to back-to-back AFC title games, though no thanks to him). Both Rivers and Smith have had good careers, but I think most would agree that, in hindsight, they weren't worth the spots they were drafted in.