I think the recommendation from Blackstone is way on the conservative side to only recommend an additional 500 miles. Did they suggest "Try an 8000 miles oil use run ..." because you've already changed the oil?
If not, my suggestion is to run it up to 10k, and sample again. The Amsoil will likely be capable of going way past that, but if you're saving money by not doing an OCI, you can afford to spend a wee bit of money ($32?) on a UOA, right? Then, if all is good, sample at 12.5k, then 15k, and so on.
The key to UOA is consistent data collection. Sure it's expensive at first, but if you're really into the understanding of statistical analysis and how it applies to UOAs, then you'll have to spend some money up front to save money in the long term. The whole point of "synthetic" oil is extended drain intervals. The only way to establish that desired criteria is to sample at fixed points along the way, and graph the results. You'll begin to see established ranges and trends. Then, you'll truly know what your safe sample intervals are.
Further, you can never just abandon sampling with extended OCI's. There is always the risk of some mechanical failure effecting the oil's health, which in turn effects the overall engine health. I would NEVER extend an OCI to 15k or 20k, without UOA's at least at 5k intervals. Fuel or coolant dilution could do too much damage if left unchecked, and it would be no fault of the oil at that point!
You've got a great looking UOA; it's a starting point for more data collection. In no way, at this point, is there enough data to support any decision on a finite OCI interval. My suggestion is always to start with oil samples at 2.5k mile intervals. Once you get 7-10 good samples, hopefully you can see good ranges and trends. Only then, can you cut the sampling back to 5k mile intervals, and leave it there until a UOA establishes the oil has reached it's end of useful life.
Another thing to consider is your total mileage per year versus the total cost of UOA's and EDI's. If you're only driving 10k or 12k miles a year, then UOA's and EDI's probably are not even cost effective for you. If you want to do them because they are "fun" and you enjoy the BITOG experience, that's great. But to TRULY use UOA's, you should be working towards the intended purpose of monitoring lubricant health.
