If you mean the Col de l'Iseran its 130km by road from here.
We were going to go that way but there isn't time now if we want to catch the Etape Tour de France and the real Tour de France down near Alpe d'Huez. I've done most of the highest ones. I prefer the smaller ones to be honest. Generally better scenery, usually but not always better weather and I definitely prefer the narrower roads with lots of switch backs. Col du Tourmalet and col du Tentes are the highest ones we have done on the bike at around 7000 and 7200ft