I currently have Tiagra front and rear with 105 shifters. A couple weeks ago I rode a friends bike who had Ultrega SL brakes and shifters. WOW, what a difference in stopping!! I ride alot in traffic and the ability to stop quickly is very important. Would upgrading just the front and rear brakes to Ultrega SL make a noticeable difference or would I need to upgrade the shifters as well?