this works, correct? thinking of getting a 10 spd Shimano 105 shifter with an existing Ultegra 9 spd der and cassette. just want to make sure it would work. can't think of any reason why not because the shifter just shifts the rear der one "notch" without regard to the distance shifted, correct? I just wont' have a 10th cog. So theoretically I could use a 8 spd shifter on a 9 spd system. Am I thinking about this correctly? Thanks!