Mulaka,
Most of my local customers run their Amsoil for a full year, with a filter change and topoff halfway through, and NEVER do an oil analysis. They also don't "dope" their Amsoil with Lube Control, Auto RX, Schaeffers #132 or anything else. I strongly advise against this practice as it voids the Amsoil product warranty. I have seen negative effects from mixing Amsoil with certain oil additives like "Marvel Mystery Oil" - I think it's asking for trouble.
Based on the oil analysis testing I've done over the past ten years, I personally recommend a change interval of "only" 15,000 miles/1 year for the regular 5w30 or 10w-30. If you use the Series 2000 or Series 3000 oils, you can extend that to 20,000 miles/1 year, with a filter change @ 10,000 miles/6 months.
As a general rule you can run the longest drain intervals in non-turbocharged, fuel efficient, four cylinder engines. Big V-8's and turbos degrade the oil much faster, but for different reasons. I wouldn't exceed 15,000 miles in a V-8 or 10,000 miles in something like a VW/Audi turbo engine.
Running 25,000 miles/1 year will get you excellent long term results. However, my goal is to get my customers optimum results, ie 250,000+ miles while retaining "like new" performance from the engine.
I feel the shorter 15,000 mile/1 yr change intervals keep the engine even cleaner internally, which is the main reason I recommend it.
If you have any questions, any of the Amsoil dealers on this forum will be glad to answer your questions.
TS