From all the choke testing I've done with Indian Creek, a .570 gives the closest 250/250 pattern.  The .568 is going to be around 275/240.  My 870 with the IC  .562 shoots 300/230.  That should give you something to start with.  If you really want a shooter, the .555 does 370/200.  You might want a red dot or scope for that one.  Hope this helps.  Good luck!