Ice, I know you love your Mitsu, but do you really want to drive it on such a (supposed) spectacular road? Maybe consider a rental? Perhaps a BMW 3 Series? 3000 kilometers in a small car like that would be brutal, and may kill the fun.
its a good idea for the trip, i was planning a similar one and i will 100% do a trip like this so why dont make it together with as many people possible, for sure people with fast cars are in advantages, but its not important how fast is you car, but how you drive it and how you enjoy it.
1 day 5 hours yes, with a zonda...hehe...try calculating it with autoroute...5 days i think...we could meet in Ljubljana with people from here and with others somewhere in Germany or France to take the route Davos to Stelvio together...but first we could try to do a short roadtrip here to meet people and to plan the trip.