assumed he must be a dual-threat.
To be clear, he IS a dual-threat. He is not a run-only QB ala Pat White or somebody like that.
Guy has the size, speed, and vision of a Vince Young and probably a better arm, too. He has incredible upside.
Rettig, on the other hand, is more of a true pocket passer. He seems to read defenses well and is very accurate with his throws (more accurate than Jennings at this point, IMO).
Now who has the stronger arm? Difficult to tell. Neither of them overwhelm you with their arm strength, but both have good arm strength.