I finally tried some Klip Legend natural gut in my RDX 500 Mid and I have to say it's an extremely nice combination. The ball cupping I'm experiencing is amazing. It almost feels like I'm catching the ball on the strings and throwing it back when I hit the ball. Also, the Legend has added some much needed power to this frame. I'd recommend this setup to anybody still using the RDX Mid. Right now I'm using 16g at 55 lbs. I might try the 17g next time.