I don't think Mega Ray Ray is going to be that good in standard. If anything, the next format will strengthen Giratinia. It will be dumb luck if you get the hex and Lysandre in the discard on T1.
So ya, If two Giratnia's hit the bench Ray Ray will go on his heels quickly.
Here is how I would run the Ray Ray deck. Your better option is to play Ray Ray with Xernias Break. With 4 energies on the board you will 80*2 = 160 on giratinia. Garitinia is weak to fairy. Unfortunately, once you break into him the fight furry belt mutes. But instead of fighting fury belt, run max elixir. With one more energy on the board, you would have a really good shot of OHKO Gartinia on turn three, or if you go second turn two. But besides that match up, Xernias break will be a very reliable attacker because there is a good chance you could hit anywhere between 80 to 120 points of damage while charging up other Pokemon on the board very fast. In this meta you are going to want play more from your deck than your discard pile because your discard pile will be unreliable. I think super rod will be a pretty big card in the meta to get things back that you really didn't want to throw away.