I have wear rate data generated from thousands of UOAs on several light-duty diesels; 6.6L Dmax, 5.9 and 6.7 Cummins, Ford/IH 6.9, 7.3, 7.3PSD, 6.0PSD, 6.4PSD and a tiny bit on the 6.7PSD.
On a "per mile" basis, the 6.6L Dmax has the lowest wear rates as an overall engine family. However the 5.9 Cummins is a near-tie, and the 6.7L Cummins is not far behind. Much of it depends on use; you cannot look at Fe and not take into account service factors.
But ... I've not seen UOA wear data really be able to predict the end of life for an engine. Take, for example, the 7.3L PSD ... it sheds a fair amount of Fe and Al, and yet those engine (when not grossly modified) are very well respected for longevity, despite the metals they throw off.
Want to make an engine last? Pick an engine family of good pedigree; no sludge issues, no cracked heads, no cooling issues, etc. Then, just follow good routine maintenance practices. The diesel will last longer than you likely will drive it.
Conventionals vs. Synthetics isn't about which is "better"; it's about which lasts longer, while assuring safe operation, in relation to cost. Any product can be over or under utilized. The same applies to filters.
Make an informed decision; first consider your operating conditions, next determine your maintenance plan, and then pick your lube and filter. Don't do it the other way around ...