I think that you need to look at certain target schools and see where the student stands. I think that aiming for / being at the 75% percentile is a good place to be absent any other hooks.
Let say you take the same student with a 3.8 UW GPA and a 4.4 weighted GPA. Is getting a 1300 a problem on the SAT?
School A 3.6 - 3.8 25%/75% UWGPA and 1250-1290 25%/75% SAT
School B 3.6 - 3.8 25%/75% UWGPA and 1350-1390 25%/75% SAT
For School A it would appear not to be a problem. For School B, the student is hurt by having a 1300 SAT.