I changed my oil/filter today at 6.3K miles. Decided to switch to Idemitsu 5w30 and OEM filter. Here's a picture of a Royal Purple filter (L) next to a Mazda Thailand filter (R), both are new, the plastic cover on the Mazda was removed. Similar size, the main difference is the pink silicone diaphram on the RP filter to prevent drain-back. I learned in September that we don't need no diaphram, we don't need no drain control. The used filter is also RP and will get cut open this weekend.
Having read another forum discussion about synthetic oil, I am going to stick with shorter OCI (6K and hopefully 5K). Even if the oil/filter can last as long as 10K or even 20K, it is better to let the engine use cleaner oil/filter. How often do we change our bath towels? We won't get a rash if we wash it once every two months, but once a week is surely better for our skin.