Wow, you have real blotter paper, not the white file cards I use. I like to look at the blots held up to a light so you can get a good look at the middle. I don't see any ring formation at all, just the color variation between the drip area and the bleed area.
I tried scanning the paper on my transparancy scanner (with back-light), but the paper texture was obscuring the detail. The flatbed scanner yielded a better result.
Actually, the center is really darker. I suppose the oil gets filtered by the paper while the stain spreads. I plan on scanning a new sample every few hundred miles.
I am using index paper, no cards, to do the same with mobil 1 0w40 on my 95 BMW 525i with 107,000 miles.
After almost 3,000 mile the blotter looks almost the same as your 800 mile blotter, perhaps a bit darker. I find that the oil continues to spread over time and looks lighter. Even so, the oil on the dipstick looks dark brown.
I am glad your blotter looks similar to mine. I may also try mobil 1 5w40 truck and suv next.