For me, the T Road Pearl is about 5 feet longer, with more snap on the backend.  My T Road Pearl is drilled 5 3/4 pin to pap, pin drilled out in middle finger.  My Illusion is drilled 5 pin to pap, pin below the bridge.  I like to use the T Road Pearl on lighter volumes where I need something to get down the lane further.  I like the Illusion on more medium shots.  However, a lot of the Illusions we've drilled in the 5 to 5 1/2 pin to pap range above the fingers, seem to get down the lane quite well and arc hard off the spot.