Thanks for the good advice, guys. I have decided that whatever I do, I'm not going to rush into anything. After all, my D300s is doing a great job. And I can handle doing musicals with only one camera. It's just more convenient with two.
I read somewhere the rumor that Nikon will make several more new model announcements before the year is out. Hopefully, there will be a D300 replacement. I expect that it would have native ISO 6400, but 12,800 would be wonderful.