Yes, this was my first thought. If I was seriously stressed for time, then I'd agree with idea of optimizing for overall percentages. But if you really want to

Yes, this was my first thought. If I was seriously stressed for time, then I'd agree with idea of optimizing for overall percentages. But if you really want to optimize the chances that a specific person will reply to you, then it seems as if longer is better. Still, I'd like to compare a short, witty, well-crafted, personally tailored message to a longer, more-generic one. (Not that that could be measured statistically...)