It is relitive....
I'm knocking on 300,000km on a 4.2 straight 6 no turbo. Most of these km's are hard overlanding (Africa, Russia, Mongolia, Outback Australia).
I swear by the 'No Turbo, No Power, No Problems' saying, but I have to admit, sometimes it'd be great to have that extra bit of grunt.
So even though I don't have a turbo, I'd say if the vehicle is in good check before you set out, you should be ok. Also depends on the year of the car and how it was treated.