505c2  http://www.trackbowling.com/products/balls/mid-performance/505c2
asymmetric core, lower diff, lower RG, earlier and weaker, more of a sharper motion downlane

tourX  http://www.trackbowling.com/products/balls/mid-performance/tour-x
symmetric, higher diff, much higher RG - longer and stronger, more round

generally speaking, layout and surface can make these quite a bit different