I've made the trip to LIM from SFO on a Star award in C. SFO-MIA-GRU-LIM and back. UA on all but the GRU-LIM-GRU flights. It was a lot of flying - 5 hours to MIA, 8 hours to GRU and then another 5 hours up to LIM.

Now that the MIA-GRU routes no longer exist, you'll have to go through ORD or IAD if you fly UA.

AC award availability using UA miles is notoriously hard to find.

I purposely avoided the RG routing through LAX b/c I had heard nothing good about their C product.

I may visit LIM again this fall - this time, I'm going to try for an F award from LAX-GRU on the ex-Swiss MD-11 which is supposed to be nice. Second choice will be on AC since I've heard great things about their international business product. If neither of those work, I'll take the long way on UA in C -I don't think F on the 767-300 is worth the extra miles.