Hi there,
I've actually done the opposite and changed from sport tour to a tour. From my observations, if you keep everything else the same I don't think you'll notice the difference. I'd be more inclined to have the wheels rebuilt with some lighter rims like Mavic 717 for example. The tour frameset is much more versatile in my opinion, I found tyre choice rather limited with the sport tour but there are several more Schwalbe tyre available to suit now.
Cheers,
Steve