Choice to make in regards to XO Twist shifters to X9 rear Derailleur or stick with the XT rear derailleur that I currently run with the Attack twist shifter. I've run the rockets wit the XT rear but I really don't like the shape of the grip for the rockets. Performance wise, I thought it was fine. Will I see a significant performance gain going with the XO/X9 setup? $140 for current 07 models shifter and rear derailleur compared to $63 dollars for just the attack twist shifters. Thanks in advance.