I think it is a smart move to take it twice. I took the GRE twice a couple years ago (September and October as well) and my second time I scored significantly higher. You get to have a "practice run" - you test under a time limit, see real subject GRE questions, etc. I also saw some September questions on my October exam and was able to answer them quickly because I had already done them before, so that was a bonus.
As for reporting, I waited until I had my scores back and then chose which one to send. The drawback with this option is that it is expensive, $25 per school. I am taking the GRE again this Fall and I will report to the schools on test day, it will save me some money.
You could report both scores on your testing days, I imagine the schools would take the higher score of the two but I am unsure...I wonder if anyone else here has experience with this option?