I've been running Amsoil full synthetic 5W30 since the car had 2000miles on it. As I don't drive it as much as I used to (9-10K miles a year), I change the oil once every two years. Last July when I changed the oil and filter (all installed for two years), I only added 1.5 quarts over that two year period, and 1.5 years in, I sucked some oil out and sent it in for analysis. The results came back and it showed 32% oil life remaining with very minimal deposits and the oil was well within specification. In June, I had put 18,700 miles on, and the oil is rated at 25,000miles (or one year - but I let it go longer). This is the second time now I've done a two year oil change with no ill effect on anything. Next year, when it's oil change time again, I'll pull off the valve cover gaskets and take some photos. I might even drop the oil pan depending on how I feel that day and check for any possible sludge deposits.
To date it still starts and runs fantastic. I just rolled over 52,000miles this week. I blame the lower than usual mileage on a recent 2012 200 V6 sedan purchase - ha. As that car is under warranty I'll change the oil each year as per Amsoil guidelines.
'11 Ram SXT 4x4 quad cab - 5.7L V8; 128,200kms
'09 Malibu 2Lt 3.6L - 140,000kms purchased 1 March 2019
'06 Pontiac G6 GT - 3.5L V6; 162,000kms (rear ended 15 Feb 2019, and given totalled title by insurance)