Axelwahl, SME makes a 'headshell spacer' to solve the problem you're having. I use one with my Transfiguation cartridge -- most modern MC cartridges are rather short (heightwise) and the back of the armtube invariably will hit the edge of the record when the arm gets near the end of play.
overhang, The Rega RB600 shouldn't suffer from the SME's problem (fat armtube ;-) however you might want to check out the lift mechanism to make sure that:
a. It's falling away completely when in the down position, and
b. the curved lift pad is perfectly horizontal and isn't bent up a bit, allowing it to make contact with the bottom of the armtube near the end of play.