NO rule of thumb when or if they will spit although #3 and #4 seem to do it more than any other cylinder.  ALL 2V's can spit a plug, they did add threads in '03 but it still happens, my CVPI is a '08.  3V's until mid '08 had the plugs that stuck in the head, carbon built up underneath the threads and that is what kept them stuck in the head, didn't help that the plug was a 2 piece design so it broke easier.

I've got about 400K miles on 2V modulars and only spit 2 plugs, one took the threads out then spit the insert a little over a year later, the other threaded back in and has been fine.