Matt Barkley is clearly the first QB gone while Geno Smith and EJ Manuel are probably the next closest to first round possibilities. I'd watch out for Tyler Bray declaring and shooting up the board like Tannehill last draft. He's got NFL arm talent and he will likely impress in all the pre-draft events and work outs. Like I said, there are really only 4 teams that seem potentially ready to take a QB early. With so many "upside guys" like Klein and Matt Scott available after the top prospects get drafted, McCarron going in the 4th round or later is highly likely.
The competition for being a top QB taken in 2014 is so much better for McCarron, he shouldn't even be seriously considering early declaration. Aaron Murray, Bridgwater, Mariota, Manziel, and McCarron would be the best returning draft-eligible QBs in the 2013 season with Murray and McCarron being the ideal NFL QB types of the group.