Go with Tourances or similar 'tarmac' oriented tire - longevity on pavement is better than having knobbies for the bit of dirt you do (and less vibration, less tire noise on pavement).
You can do the entire distance Santiago to Ushuaia on pavement (except, on Tierra del Fuego, the Chilean portion) - if you don't do the bit from Baho Caracoles south to Tres Lagos on Ruta 40 (this, IMO, is the worse stretch). And that is now probably close to half paved.
And if you just keep your speed under control, this stretch isn't so bad. Its when you're doing 100kph or there abouts and you go from one sort of gravel to another (thin and hard, to deep and soft for example) that seems to be the problem for most people. They get complacent, speed gradually increases, and wammo - big winds, lose gravel, maybe a off-camber corner - and bike or body is bent and broken. Otherwise, Ruta 40 isn't that hard.
And BTW - Ruta 40 is more like 75% paved, less than 25% unpaved and shrinking fast, and that's the entire length. There's spots in the north, north of Cafayate, that are as 'bad' as in the south. Just not as windy.
Doing the Caratera Austral isn't a solution - you still cross back into Argentina and ride the Bajo Caracoles to Tres Lagos portion.
Chiang Mai, Thailand