Take a look at the back of your owners manual...all the capacities are listed there. As for royal purple or redline...the jury is still out. I've heard good and bad about both. Some say RP is too slick, others swear by it. Hopefully someone will chime in with a biased opinion supported by data.
I'd suggest that your money is better spent on Dexron III and using the savings to change your fluid and filter on a more frequent basis. Mike at Yank has said that some aftermarket oils are too slippery for the clutches to work properly in high HP cars.