Here's my advice to anyone who is a flash animator: The lower the version, the better. The studio I work at runs completely on CS3. Flash has neater tools as the upgrades go, but those tools are all for actionscrtipting and are otherwise flawed vector updates. Adobe tries to claim flash isn't for animation so with each update they make it worse for animation.
Also, when you're working with any traditional animated file, try to keep the length of your flash around 50 seconds long and then use another program to bring it all together (Final Cut, After effects, ect). This way you will be able to work on individual scenes and flash will never bog down. This is the best way for handling flash.
If you want to keep it all in 1 FLA file, I suggest splitting the flash up still and then copy pasta that shit into 1 file when you finish it!
... Also, save often!