Best route & best day to get round Paris?

We were going to head South from Calais via Rouen with the aid of the excellent Valda's 'Idiot's Guide', but now OH would like to detour to see his G/father's WW1 grave near Albert, which means it's more direct to use A26/E15 & then on round Paris towards Nevers.  Google & Via Michelin both direct us via the peripherique, but I'd rather turn off past Chas de Gaulle Airport & past Disneyland on the N104 towards Evry if I must come so close to Paris.  I wonder if there is a way I can programme our new Garmin nuvi 2595 Sat Nav to do this?  I usually use towns/villages but that doesn't seem possible on this route.  Are Saturdays & Sundays quieter? Or as it will be the week-end 25/26 May - the beginning of half-term, shall we steer well clear all together??