Lets not throw out Randy Johnson comps quite so quickly, even it was meant to be tangential. Their bodies are nothing alike, they throw from different sides, Randy threw 5+ mph harder (a bigger gap if you normalize that to respective league averages) and had maybe the best slider in the history of the game. We might as well throw a Mantle comp on Pompey.
Kyle Drabek or Tyler Matzek are far, far more likely outcomes than Randy Johnson.