I don't know the RCS of any plane, but the effect on range is easy. Look up "radar range equation" and you'll see detection range equals the 4th root of the product of several parameters, one of which is RCS. If you cut RCS in half but all other parameters are unchanged, detection range changes by the 4th root of 0.5, or 84%. This 4th root behavior is the reason a very large RCS reduction is necessary to get a big reduction in detection range.
As soon as I posted that I realized it was badly worded. It gives the impression a 50% cut in RCS reduces detection range by 84%. I should have said detection range is still 84% of the original range, i.e., not a big reduction.