Just my win10 opinion but I don't think there is any significant difference between RC8 and RC 9 anyway. I sort of treated the upgrade to RC9 (~us$45 at the time) as more of a donation than a purchase, lol!
I would do the same - but on the Mac Appstore, the upgrade price from RC8 to RC9 is about USD170! (It is perversely more than just buying RC9 outright).
Still, I'm getting lots of use out of RC8 on my mac - I'm lucky to have it because Aerofly RC is far superior to anything else running on a mac.