Unless you just want to spend more money to get less in return I would stay with the 105. The 105 is a tad heavier due to using some steel parts rather than alloy and the 105 is not as well polished. If you get really into racing then skip the Ultrega and go on to Dura Ace. BUT I also knew plenty of riders that clubbed raced on 105 and they found them to be dependable and cheap. But the Ultrega is basically a glamorous 105.