smer,
In my opinion the coverstock, and any adjustments made to it, affect ball reaction more than the core will since that is the part of the ball in contact with the lane surface.
The core can enhance what the bowler puts on the ball, and can compliment a good cover, but the bowler's style (revs, speed, tilt, etc.) and the cover will have a bigger influence.
Every company has made some great equipment over the years, especially when it matches up well with the bowler's game and conditions. There are certain balls that are literally "duds" for me, but may prove valuable for the next guy.
So, if you've had success with a certain coverstock, and even certain layouts, it's hard to argue with that. Roll with it!!
--------------------
Lane Carter, Strike Zone Pro Shops - Salt Lake City, Utah
Brunswick Pro Shop Staff
www.brunswickbowling.com