OS X El Capitan is still not a supported OS.
Also, there are some performance issues that we have noticed with R9 card(s) which has been reported to the concerned team.
I will suggest you to wait for the final release of OS X El Capitan and then report the issue(s).
Thank you, Vinay.
I know this is not final version of the OS, though it's the GM Candidate.
I'm sure this is related to the AE card support issues you refer to.
Ok, I will wait the update from Adobe.
This is not related to the R9 card as After Effects might not use R9 card(s). It is all about the Beta version of the OS X for which we cannot provide much helping hand.