I respectfully disagree. Tannehill isn't a "project." He's just not very good. Call it what you want, limited upside, low ceiling, the dreaded 'system quarterback'. He's just a guy. And you don't use first round draft picks on "guys."
Tannehill's got serious limitations with his arm and pace. He's a good athlete, but he's sluggish in the pocket. The time he takes from decision to delivery, including that hitchy throwing motion, makes for a long uphill climb in the NFL. He's going to get the ball knocked out, knocked down, and picked off at the next level. He's just too deliberate.
He also has a tendency to lose his fundamentals when he's moving. He throws open (without turning his hips) when he's going left, and throws across his body moving to his right.
He's a smart kid, and a better athlete then most of his contemporaries at the position. But you're looking at a career back-up unless something changes dramatically. Best choice... he's a mid-2nd to 3rd. But he'll go unnaturally high due to a shallow quarterback class.
Without respect to need, I've got a 4th round grade on him... but, in the NFL quarterback lust is worth about a round and a half. And the rookie wage scale makes it more palatable than it has been. But, he'd be over-drafted in the 3rd... much less the first or second.
And I'll argue that there are two quarterbacks deserving to be the top 10... actually there are two worthy of the #1 overall. And I'm not sure how you figure that RGIII is a "project." That kid improves 25 NFL teams tomorrow, if you throw him in the lineup.
-jj