Will a Flash 9 SWF perform poorly in a Flash 10 player?

I created a Flash video player a long time ago when Flash 9 still had a sizable market share. Now that nearly everyone has Flash 10 player, I am wondering if I should publish as Flash 10. I don't believe that I'm using any level 10 开发者_开发技巧API calls, because my Flash compiles fine at level 9.

1. Is the performance of the SWF determined by the client's Flash player or my publish version?
2. Will Flash 10's video hardware decoding not kick in if I publish as Flash 9?

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If it publishes and runs fine on 9 then you will notice no difference on 10