Sludge is a term for oxidation and insoluble residuals that manifest into "goo" and such in various engine hiding places. Don't confuse sludge with varnish. Light-to-moderate discoloration in very thin layers on surfaces is just varnish and generally harmless. True sludge is the thick gooey/gummy stuff you see in advertisements signifying the onset of horrors ... Also, don't be alarmed to see some very dark formations in areas where oil pools in pockets; that is totally normal and harmless.
Both the ox and nitration levels are up just a bit on your sample; those can be indicators of contributors to sludge. Now, since we don't have a VOA handy to know the starting points for those criteria, we really can't know how much shift has occured. I'm not inferring you should panic or otherwise be alarmed. I bring this up as something to watch for. Given those numbers, I'd think it would be prudent to take a peek under the valve cover at some point in the near future and just see how things look. Your soot is admirably low, so that's not a concern.
Extended OCIs can be a great savings tool, but they are not something that can be done sort of "halfway" and also be done safely. Not only do you want to do UOAs, but also monitor inputs like fluid levels (coolant, oil, etc) and then also make visual verifications (looking for sludge onset, leaks that may develop, etc). Compression checks are a good idea, but they are difficult on a diesel; easy on a gasser. Etc, etc.
You have a great history on many pieces of equipment showing extended OCIs are viable. This would be yet another. But don't be lured in unwittingly just by the UOA only; use other tools as well to confirm the overall plan is working well.
Your wear, as I said previously, is crazy low. Nothing has had effect on the engine yet. I'm just offering one point of contention to watch for. It's not an assurance of sludge; it's a cautionary note that you should heed to check for sooner rather than later.
Next time, consider a VOA at the onset of an OCI, so that you have some base numbers for comparison. If you are buying in bulk, and still have some of this lube load sitting virgin somewhere, you could send it off to get the info now. You are saving so much money with the extended OCIs, you can afford a VOA once per drum or cases of lube.
Hope I haven't made you wary; just trying to help you have a fully-informed approach to your maintenance plan.