I'm posting this as an OKT out and back, although it could be broken into an ascent-only trail as well. Even more popular than this route is the full 40 mile Huemul Circuit which continues the trail from Paso del Viento to the Viedma Glacier, Lake Viedma, and finally El Chalten. This was the most beautiful and dynamic terrain I've ever been on, and it is virtually untouched by runners (I only know of four reports including mine, that attempted to run any portion of this trail) although backpackers are a bit more privvy to it. My OKT won't stand for long, but I hope it gets the attention of more serious runners into this gorgeous area.
[Admin note: Adrienne's Strava track starts & ends in the center of El Chalten, adding about 1km each way to the total distance, and maybe 10 minutes to her total time. Judging from her GPS track her time from the Centro de Visitantes would be about 9h22m08s.]