The mod motors are generally very reliable. 500k miles is certainly attainable barring any unforseen event.
Interesting note: I spoke with the manager at that Total Tire store which did the service for the Ford F-250 that I linked. It had over 3 MILLION miles on it when it came out of service a few years ago; it was wrecked in an accident. The original motor only went 100k miles, and was replaced by a motor from a salvage yard; that salvage motor went more than a million miles, and then it was replaced with yet another that went over a million miles, then two more that went until the truck was totalled.
My point is this ...
That first motor went out at 100k miles; when I asked no one could recall why. But as much as that guy drives, there was no time to have a down vehicle; they could not take the time to rebuild it. So, it was a race to find the first available 5.4L replacement and get him up and running. Given that he was a devout customer, and they never changed any operating patterns, then it's likely the engine oil/filter was not the cause of the first motor failing. If they had used inferior lubes or filters, that failure mode would have likely re-appeared later in either of the two ultra-high-mileage motors. Whatever made that first motor fail was more likely a manufacturing defect or catastrophic material failure.
BTW - they used Kendall bulk 10w-40 and Purolator Classic filters for all his maintenance. No syns, no Pure One or Ultras, etc. Just routine OCIs at around 7.5k miles (give or take a bit due to his weekly driving delivery routes). I asked if he'd ever given consideration to using syns or bp filtration; nope - he just wanted routine O/FCIs and he was on the road again. I'm sure, given the kind of constant customer he was, that he got preferential service upon rolling up to the door. They kept him in tires, LOF, a/c service, etc; they are a full serivce center with ASE folks on staff. After wrecking that one 3m-mile truck, he now operates two used 7.3L PSD Fords for his business. I find it interesting that most ultra-high mileage daily vehicles actually don't use syns or BP; most just see frequent O/FCIs. (I am excluding OTR tractors; I don't have much experience with them so I cannot comment on that).
So this is the take away from these type examples:
- no oil or filter, no matter how expensive or great it looks on paper, will ever stop an impending mechanical defect.
- normal products have the ability to make equipment last far longer that most folks will ever operate.
- premium products can save you money, IF you know how to manage the cost ROI.