Unfortunately I don't have the confidence that you do about Dayton and Montgomery county.
Honestly I don't have the confidence in Clark county either, but I figure that Brown is the bigger unknown and that alone will push DeWiener through.
You need to understand that Dayton proper (like Cleveland, Toledo, Akron) has been losing population by leaps and bounds (1/3 since I came here 20 years ago!!). The overwhelming majority of that lost pop. is DEMOCRAT, because it was blue-collar/industrial. Whatever pop is coming into Mont. Co., Greene, and Warren, is white collar/technical/managerial---far more likely to be GOP. So not only can you not just look at the registration #S, but, like Jay Cost points out, you have to look at the pop. shifts.