Clinton by 10 pts. If Giuliani is the Republican Nominee...he will bring states into play that aren't supposed to be in play, like Connecticut, New Jersey, Minnesota, Michigan, and would probably take Ohio, Pennsylvania, and Wisconsin. Florida easily goes Giuliani. It would cause Hillary to have to make stops in NJ, CT, MI...places where she probably wouldn't have had to in a say...Clinton vs. Romney race.
Or a Clinton vs. McCain race.
You pretty much summed up every reason why I think you ought to support Giuliani in the primary: because he can win and give the Democrats a run for their money in states most Republicans wouldn't normally carry; that's something no other Republican in the race right now can do.