This is a good question..... coincidentally 2 was ago I decided on these 2 and purchased the black widow spare for a strike ball (can't keep reactive on the left side of the lane right now). To me, if you changed the surface of both drilled the same (pin up for me) the bws pushes slightly farther down with a slightly more angular move, where as the track spare+ (Padarox core). Is rollover and more forward/archy smoother on the back, and a board or 2 less hook.
Please keep in mind that I purchased this as a STRIKE BALL, and NOT as a spare ball, I still believe even comparing them going straight that they both will go straight (oob) but the bws will still wanna move a little more at the end (unless you have total control, or are speed dominant). Just my .002