It would seem like there should be additional ppm of metal in the oil, maybe not double though.
Also does gearing affect wear rate?
For example, my 350 Caprice has the trailer/performance gears, 3.42's. Compared to a base model with maybe 2.56's I am turning an additional 400 rpm on the highway.
Because the 5.0 has twice the displacement and twice as many pistons as the 2.5, that wouldn't actually mean the wear will be linear. You may see more wear, but engine design has a lot to do with it. Does the 2.5 rev higher? What is the total bearing surface for each engine? What is the power / displacement? V8s and I4s have very diferent wear patterns as well. You may see more iron wear in the v8 and more lead wear in the 4. OHC and OHV engines wear much differently too.
Also the applcation would dictate most of the wear. For example, the I4 may be in a Ranger with a 5 speed that is driven by a careless teen. Frequently lugged and run up to a redline of 6K. The Ranger may be driven a full throttle when stone cold. The V8 may be in a Grand Marque (sp?) and driven by a little old lady, max engine speed of 1800 RPM. The little old lady always warms up the car and goes for long enough rides to sufficiently burn off the moisture and fuel.
So its very hard to say how engines wear compared to differnt makes and types. The best way to pattern is to evaluate only identical engines. Then evaluate the driving conditions.
No, The wear metals must be compared to other engines in that same family. Their is not a direct linear correlation to wear based on engine displacement or number of cylinders. Now fuel dilution, oxidation and nitration might well be different.
I have seen Lexus V8's running cheap oil show much lower wear metals then V6's made by other manufactures and some 4 cylinders as well. THe engines design and material selection in combination with the companys assembly standards has more to do with wear metal then the displacement or number of cylinders.
If you have a poor engine design combined with cheap materials and average to poor quality control you end up with an engine that throws wear metals like crazy even with the best oils. It would not be fair to compare that type of engine to another brand of engine! You would have to compare it to like engines from the same manufacture of identical or simalr design.