Regarding point one you make, Pablo, I'm not convinced that a syn would be "cleaner" internally at 18k miles. Cleanliness is predicated upon the initial level of "dirty stuff" in contamination rate of soot/insoluble production. To say that a syn would make this engine cleaner at 18k miles is to presume two things:
1) the engine was dirty to begin with
2) the engine is producing contamination at such a rate the dino oil cannot keep up.
We don't know that either condition is true. What we do know is that the soot/insoluble count in these four consequtive UOAs is very low and controlled. So, my point of contention is that syn's cannot clean up more than a dino, if that level of contamination is not beyond the ability of the dino. If the VPB add-pack is not overwhelmed (which it clearly seems to be working as designed) there is no reason to think that any syn could do a "better" job at cleaning up stuff that is already under control. All indications are that the VPB has things under control; the add-pack is strong and stable and the soot/insolubles are low, in a consistent manner from UOA to UOA.
Time for one of my famous analogies:
You can hire three maids to come clean your house once a week, but if you are living at home alone, and not making a big mess, then only one maid is needed. The other two are superfluous; they cannot clean up what's already cleaned up.
You're making an unfair assumption that the dino oil isn't keeping up. We have data (TBN, detergent/dispersent numbers, insolubles numbers) to show things are under control. You can't clean "better" than what's already under control.
As for my "60k miles, no top off" comments, I was calling to note that the VPB has the clear ability at this point to do 20k miles, with no bypass filter and no top off fluids. If any syn were to be worth the 3x cost factor, they have to be able to triple the experience. As soon as you were to add a bypass filter, or start adding a bunch of oil in top-offs, you further drive out that ROI point of equality. The "3x" factor would work closer to 3.5x or 4x to "break even".
Yes, I agree that this series of UOAs shows that there are times when Fe is simply an accumlated phenomenon. And I also would think that by 20k miles in this engine/oil/filter combo, it might be to the point that condemnation of the oil is warranted, even if other wear metals and such are under control. In the other Amsoil/Dmax UOAs we've seen, I've never stated that there is 100% proof that Fe is clearly a direct result of Cu abrasion, but I did say that we cannot prove it's not. The difference is in the proven/known versus the suspected/unknown. In these UOAs of VPB, we can assure ourselves the Fe is not due to elevated Cu, because there is no elevated Cu. In some Dmax/Amsoil UOAs, we're left only with presumption, and not fact. The differnce in my tone is what's known versus what's possible. If in the past I've stated that there is 100% knowledge that super high Cu causes elevated Fe, then I was wrong; but to be honest I doubt I ever said that. What I have said multiple times is that we cannot simply exclude higher Fe in an Amsoil/Dmax UOA simply because we don't want to believe they may be related. The differences are in the nuiances of possible/probable/definite.
As for your point 2, I fully agree that at some point, the syn will outperform the dino oil in a UOA. By "outperform" I'm going to say that includes wear metals, insoluble control, TBN retention, etc. But I will EXCLUDE fiscal review from that comment. And that's where the whole syn vs. dino topic sits. ANY oil can be under or over utilized; the point is to use any lube up the it's condemnation limit, and then OCI. Would this VPB start to degrade at 20k or 25k miles? Most likely so. Would a syn outperform the dino after that mileage? I'd certainly like to think so; I'd bet some money that (at some yet unknown mile marker), the syn will clearly pull away in wear protection and such. But, at what point can you say it's "worthwhile" to pay for the syn? That is where the ROI comes into play. Which is "cheaper" for the "same" protection level? (I'm going to pick some artifical numbers from thin air; don't skewer me please)... If you set a limit of 50ppm for FE, or 15 for Cu, or (etc, etc) then you run the oil up to those condemation limits, you simply look at the duration of exposure as a factor of cost. If the dino oil can go 20k miles, and then be condemed, that is your marker point. If the syn can go 40k miles before condemnation, that's certainly longer. But is it "better"? Not if the OCI factor is 2x but the cost factor is 3x; it's simply cheaper to OCI more often with dino. Remember, the whole point is to run either oil up to the same condemnation point, so the ONLY variable is duration of exposure. Then the "better" oil is the one that provides the needed level of protection for the least cost; it might be dino, it might be syn. Only the safe, effective OCI duration will determine which is "better", based not upon some arbitrary "I can't keep my hands off the wrenches" approach, but rather a "I'm going to get the full value of my purchase, regardless of base stock" approach.
In this situation, I don't think there is a snow-ball's chance in Hades that a syn could go 60k miles unassisited by top-off or bypass. So, that would drive the ROI cost factor up to perhaps around 4x? (I'm incluidng initial cost of bypass system, replacement filters, shipping, etc). So a syn would have to go 80k miles with bypass to break even on cost. Certainly can be done. Question is this: will it be done?