Creating a custom aggregation for views
Whether this is the best, I don't know, but it is pretty easy:


Create a new field called handicap.  It doesn't need to have any value as you will be computing it.
Create a views template for that field.  It would be something like views-view-field--field-handicap-value.tpl.php. If you want it specific to the view, you will need to include its name in there as well, but just look in the Views Styles/Themes to find it. 
In that template, do your custom aggregation function, and then output that result instead of the default $output.


Now, if all is good in the world, you will have your handicap output in the view and you can aggregate on that value as well later on in the view, too.