In reply to Jack Geldard - Editor - UKC: Think your examples of putative french grades for trad routes are pretty unrepresentative (was that the intention?).
Ok, lots of E5s might be F7a (though lots are much less)
E6 is usually 7a+ (though there are a few E8s eg. Countdown to Disaster, The Complete Scream which are 7a+). Strawberries at F7c is hardly representative of E6s!
Most E8s and E9s seem to be around F8a/8a+
E10s seem to be around the 8a+-8b+ mark
You are allowed rhapsody I suppose as there's only one route claimed at E11