Two Decembers ago dfwoods and I had what ended up to be a similar itinerary. Move swiftly (i.e. don't dawdle) through EZE and you'll have plenty of time for a bite to eat at AEP (rather a nice food court opened with the latest AEP renovations). LAN did not stick to their schedule particularly well on those flights (weather in IGR, primarily)...we had several-hour delays in both directions. They also did not have good lines at AEP or at IGR for oneworld. IGR is a typical resort-type airport...AEP is a constrained in-town airport (think MDW or LGA or SAN) with relatively limited lounges etc (primarily domestic with flights to MVD/Punta)