1st question - why?
If you are looking at increased braking power it seems to have been established that a pad change makes by far the most difference, in fact Cheesney Hawkes went from Tiagra to 105 calipers with no percieved difference in stopping.
If it is to add nicer looking components, then it is upto you.
Not 100% but I think both 105 & Ultegra only come in short drop sizes...which will fit the caad8