Much of it really depends on the conditions you face on a dailey basis.  A great 1-2 combination for medium/light through medium/heavy would be a World Class Particle and a World Class reactive.  The World Class Particle is strong enough to even play heavy oil, while the length of the reactive gives you the ability to play a drier condition, Yet both ball cover have some common ground so you can have a different look at the pocket if your not getting carry.

Based on my experience, the Terminator needs heavy oil to outshine the World Class particle, and most people never see that amount of oil, or if they do, it's rare.  On medium conditions, the Terminator is prone to rolling out where both the WCP and WCR are still solid options.  I used a WCP and Terminator today on a fresh heavy condition synthetic, while the terminator was the better ball, the difference was small.  The WCP though, wins hands down in the medium heavy catagory.  

If you truly face heavy oil conditions, a Terminator and WCR would be a great combo, but I truly feel the WCP and WCR is an incredible 1-2 punch whose only real weakness would be light oil.  A ball like the Hornet, or maybe even the Straight flush would be the compliment to the other two if you needed something between the WCR and Plastic.  Another pairing might be a combo like the Terminator and Masterpiece or Black Pearl and Masterpiece/WCR.  Just my thoughts.

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.