Tried looking at any maps / Google maps / Mapsource or similar?
The R de GA is 684 kms, crossing 16 passes of one sort or another.
Add in whatever route you want to take from Annecy to Thonon-les-Bains and whatever 'passes' you want to do.
Subtract any distance you want to cut off the end, if you do not want to go to Menton.