I think the K/9 will be a lot closer than most people think. the 6.9 K/9 JZ posted last season has to go up a bit... His first season in the majors was just over a K per inning, and he had an even better K rate in the minors. I full expect the K's to bounce back a bit.
Assuming a 200 IP season, the way that I project them to be is:
Gio Gonzalez - 12 wins, 3.70 ERA, 1.30 WHIP, 205 K's
Jordan Zimmerman - 12 wins, 3.25 ERA, 1.15 WHIP, 175 K's
Take it as you may, but I give the edge to Zimmerman.