Hi mate, Iquique to Oruro is awesome (I did it the other way). You've got about 200k's or so to the border with Bolivia (which is at about 4500 meters) , after that you have 250 to Oruro, half of which is gravel.
Alternately head up to Arica (I recommend the Party Hostel, a bit out of town but Roberto is a nutter, great time had) then you can head straight east to La Paz (In fact you come out about halfway up the road from Oruro to La Paz. Paved all the way. Both routes are spectacular. I stayed in Putre for the night.