You would be hard pressed to find a new gpu in that price range that would run dolphin better so you are set on the gpu department unless you wanted to spent more. Your ram is fine and you don't have to worry about it one bit for dolphin. You should be set to run dolphin at 4x ir and some aa so you have a nice build there.
Intel i5-4690k @ 4.6 GHz | Gigabyte GTX 970 4GB G1 | 8 GB DDR3 @ 1600 MHz | Windows 10 TP | Dolphin 4.0-6811