I have two bikes...one with 105 and one with Ultegra. I think the Ultegra is a bit smoother in shifting, but there's not a major noticeable difference in feel. I only wound up with Ultegra on one bike because I wanted to switch from a triple to a double (there are no mountains in Texas to fight with) and my husband decided to upgrade me for our 5th anniversary. Isn't that just the sweetest? Ok, all that to say...the 105 is fine and works just about as well as the Ultegra as far as I can tell...but that's just my .02

Happy riding!!
Steph