I don't recall the exact difference between the 5.2 and SL 5.2, but 100 grams sounds about right. It's not very much.

As for the wheels, these are 1500 grams, so they are 300(?) grams lighter than the Race Lites. But they are noticeably smoother going over bumps.

Not sure about the stem; it's the original setup from when I got the bike.