We've had several "synthetic oil life" discussion here in the past. I use to let mine go to 5000. But after I have read a ton of info on the net, and reviewed some very detailed analysis supported studies that prove out that synthetics actually work better than when new in the 7-10,000 range, I now let my DIC oil monitor do it'* job. It has been telling me my oil life is up in the 9-10,000 range.
Speaking of internet info, here'* an independent
lab study/analysis paper thats shows a variety of FedSpec tests and how a wide range of commercial products did in them. Royal Purple shows as a good starter, but falls behind many other brands in tests designed to show how the oils do as wear/severe duty goes along. It doesnt do so well in the long run with alot of brands ahead of it in key tests. The sure winners were Amsoil and Mobil One. I'm still going over the pages, a good read.