I think with the RDX 500 Mid, it is so easy to find tip speed, that it makes the racquet very easy to generate spin with. It also offers some nice flex and I often find flexible frames to make spin-friendly racquets.
The 89 Tour feels like it has more mass around the throat area compared to the RDX, so doesn't come around quite as quickly. That being said, I hit it a lot with Dunlop Black Widow and managed to generate a lot of spin with it. I also liked the feel of it once I got it moving and found it came through contact very well on my backhand and on serve.