Why not just go with a .260 Remington? You can run that in a long action, and a long action will let you seat bullets out to the lands. Be careful with 6.5x55 SM reamers, since some of them have very long distance to the lands, and you will not get even a 140 grain Berger out to within 1/4" of the lands. If you go that route, use a match reamer, or clarify with the gunsmith who cuts the chamber, that the reamer will have a shorter throat. If you get too short a throat, you can always lengthen it later with minimal effort/expense.