The Black Pearl and WCP are very similar balls, you could go with either and be very happy. However, the WCP can handle slightly more oil, which gives it the edge should you hit the heavier condition. As a stroker, I set my WCP up with Label drill, it's a great combination of hook, length, and control. While it's not an exotic drill that has become so popular now days, it's a great layout for any stroker.
The WCR does have more length, but it's not drastic, probably 10% over the WCP, and 15-20% over the black pearl. When used on the right conditions, medium to medium light, the ball can flat out hook. However on the medium/heavy conditions, it tends to go too long react properly. Of course, that's why you would have the other ball. Length is relative though, Lanemaster equipment tends not to be about length and backend, so the ball doesn't go long compared to many other companies, but it's very versitile. I had it drilled pin above ring finger with the CG in the center of the grip to add a little more length.