RFP: first - Bravo for some VERY good sense and attitude about the topic. You are definitely smarter on the topic than I was.
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Getting a good shave from the 8k means you've developed the skills to use a stone well enough to gain benefit from the polisher. In hindsight, I think I was out to lunch on this fact and learned it later in my honing. Only recently I thought I should have a Norton 4/8, and the shave from it was quite good. I actually like working w/ it more than the Nani 8 I've been using, though the Nani has yielded a higher level of keenness for me. I still prefer USING the Norton, and am still finding how to get as much out of it as possible.

The shave is smooth and comfortable, if not quite as keen as an edge from higher grit stones. I would say that when you can get that 'smooth and comfortable' shave reliably from the Norton - you can expect to get some higher performance from a higher grit stone. While everyone gets light-headed and poetic about their favorite natural stone for a finisher, my thinking is that a high-grit synthetic will serve better at first, and remain invaluable even after you have your own favorite natural. Not all blades are gonna like your gucci natural, and having a reliable synthetic finisher will come to your rescue at this point.

One thing members have done in the last couple of months is to send their 8k finished edge to an experienced honer for evaluation. There are plenty of member that would be happy to work w/ you this way. The ones sent to me, I'd tweak with my 8k and send back. Before I had only the Nani, which isn't a good comparo to the Norton, but now I have the Norton 8 as a guide. Maybe you could get outside feedback on the quality of your 8k edge to confirm its ready for the next stone. I would think most members would love to work w/ someone w/ an attitude as good as yours. I'd certainly be happy to.