Nice thread. I'm behind in my commentaries, and I keep meaning to say something about McCluster.
I agree that he's a better RB than WR, though he seems fluid and natural pass-catching. What sets him apart from most so-called third-down specialists is his ability to actually block, which is a requirement for playing passing downs. Most commentators simply want to pigeonhole scatbacks as third-down guys, without realizing they need to be able to either stay in to block or go out on a pass pattern. McCluster blocks with a vengeance.
He's not super-shifty; he makes slight adjustments to his momentum that carries him past would-be tacklers, but he keeps moving down field. That's not to say he can't evade defenders--he's one of the more elusive runners I've ever seen, but he does it by distorting pursuit angles and being patient with his blockers instead of trying to dart around like a firefly. He's always looking for positive yards, not highlight reels.
All the comparisons to Chris Johnson are quite apt. Johnson was one of my binkies a few years ago, and I always felt people overlooked him. Well, a year and a half later, I feel justified for giving him a first-round grade when my friends thought he'd be special teams/change of pace guy. They both go from zero to maximum speed in the blink of an eye, and both use their momentum as a weapon, both for evasion and collision. That said, McCluster doesn't have quite the bulk Johnson has, and he probably isn't a 20 - 25 carries/game kind of guy. He is, however, a surprisingly effective inside runner with good toughness, patience, agility, and balance. He's a great player, and I'd rather see him replace Faulk than any other back I've scouted in college.
Several players stand between McCluster and the first round: Spiller, Best, Devine, and possibly speedsters like Demps, Ford, and Holliday. McCluster is hot right now, but the combine has a way of warping people's memories of actual gameplay, and I think all those track guys put up better 40 times. I believe McCluster will fall because of his size and a perceive lack of a defined role. He's not a poor-man's Percy Harvin, in that he can shimmy and shake in close quarters and take it the distance, and he's considerably smaller and less accomplished as a route runner. He may be used in a similar way, and he'll be valuable to a team, but he faces the same problem I do: he's too small for people to take him seriously. I believe he'll be available in the late 2nd, early 3rd, and possibly later. I'm not at all opposed to trading back slightly and acquiring a 3rd in hopes we can snag this kid. He's absolute lightening.
DISCLAIMER: I have a soft spot for small players, because I'm a 5'7, 185# kid who's heard all my life that I'm too small for football. I'll graduate with my BS this spring, and never once have I had the chance to play organized football, though I've absolutely dominated in pick-up games, often against guys twice my size who've played in high school or college. Nothing gives me greater satisfaction than running over 6'2 250# former defensive ends and gaining their grudging respect for my physicality and power. It's my hope that players like McCluster (and Welker, Sproles, Smith, MJD, etc) can change the stereotypes of what is and isn't possible for an "undersized" player. I'll never have a chance, but I hope others do.