Carn the 'Scray

Not sure how accurate it is (and I assume it'd have to be applied to individual subjects rather than a cumulative average), but this might help: http://www.wes.org/gradeconversionguide/israel.htm

I might be well off the mark here, but have you considered exploring political psychology programmes? Could be worth looking at, especially since you're keen on the quantitative side of things.