No chance of Driveclub outselling Forza.
Even if we take bundling out of the eqaution, Forza 5 will still outsell driveclub.
Now considering that we don't live in a fantasy land, MS will bundle Forza 5 (Forza is one of MS's ost bundled games) which means it will greatly outsell Driveclub.
People are still writing off the Xbone there is going to be some crow eating come launch!