Greetings,
When I was looking at Kimbers, I had the same question you did. I wanted the adjustable sights for target shooting and inquired about the possibility of putting adjustable sights onto a Classic later down the line. Going through the Brownell's catalog at the gun shop, we were unable to come up with any that could be ordered and would work in the Kimber without having to do major work on the slide. It was decided the only way to do it would be to send it back to Kimber and have them put factory sights on it.
I ultimately decided on the Target model for that reason, plus, the tolerances on the Target model were tighter than on the Classic. For example, looking at the rear of the barrel when the slide is forward, I could see a gap between the slide and the rear of the barrel (back of the chamber). That gap is not there on the Target model, or, if it is, it is not nearly as pronounced.
I have been very happy with the Target model. I have not done any competing with it, but I plan to in time.