5 weeks is plenty.
Bogota-Quito: 3 days.
Quito-Lima: 3 days.
Lima-Cuzco: 2 days.
Macchu Picchu: 1 day (I wasn't impressed)
Cuzco-San Pedro de Atacama: 2 days.
San Pedro de Atacama-Jujuy: 1 day.
Jujuy-Ushuaia: 7 days.
Ushuaia: 2 days.
Ushuaia-Buenos Aires: 3 days.
Shipping Buenos Aires-Home: 3 days.
Total riding/busy days: 27
Any more than that is just fucking around. I mean having adventures and stuff. So you could tag Bolivia or the high salt lakes by Jama for a couple of days, or ride Ruta 40 for a couple of days, or hit Mendoza for a couple of days.
I don't consider this to be an extreme ride. Far, yes, but not hard if you like good long days of riding, which is exactly what I like. It's fairly easy to stay on good pavement except for where there's some construction and then when you get to Tierra del Fuego there might be some fun ripio for a hundred miles. Once you get past Colombia and Ecuador the roads get fairly straight and you can go as fast as you dare.