Ryan,
That works except for the last two columns. In the last two
columns, the lower the value the better.
I tried "reversing" your formula like this:

=INDEX({"A+","A","A-","B+","B","B-","C+","C","C-","D+","D","D-","F"},MATCH(J2,PERCENTILE(J2:J29,{0,0.05,0.1,0.15 ,0.2,0.25,0.3,0.35,0.4,0.45,0.5,0.55,0.6,0.75}),1) )

and that seems to do the trick.

Thanks for you help!

Karl