From what I remember, the 883R was predominantly a styling exercise - seat, paint job and on the carb version 2-1 exhaust (I think the later fuel injected version was 2-2).
There are dual disks up front too.
The XL1200S didn't look as smart but has more power and uprated suspension front and rear, and the XR1200 went further still.
I think the 883R is one of the prettiest Sportsters available.