Me and my husband just came back from Peru and he didn't have troubles coming back to US, he has an I551 temporary stamp in his passport plus extension notice, however Peruvian immigration didn't recognize the stamp and asked for his expired green card and proof of receipt that he has a pending application with USCIS. It took them about 30-40 mins to investigate and let him enter. So if anyone from India or China with a green card in process is wondering about visiting Peru without a visa, you shouldn't have a problem just show them a proof of your status with the notice.