I believe there is more to be said in any attempt to summarize what's been discussed thus far. I wouldn't say it's too early to tell - there are many in-service F150s of both variations with mileage in the range you've specified that could lend us the data needed to draw a conclusion with a high degree of certainty. However, the primary obstacle, as you alluded to in your second statement, is a lack of access to said data. This is unlikely to change while these engines are being placed in new vehicles for sale, and so without data, we must rely on our knowledge of engineering and physics to guide us. It is in this capacity that I believe the 5.0 has a much stronger argument for being the more reliable engine over the long run. This is not to take anything away from the 3.5 EB, but the ecoboost simply has more critical variables in play, which consequently leads to a higher probability of error or malfunction, particularly past the 100k mile mark. Additionally, while the ecoboost's greater vulnerability may not lead to a terminal malfunction event, it will undoubtedly lead to a higher probability of a malfunction, which thus enables us to reason that the 5.0 NA V8 is more likely to make it from 100k miles to 200k miles with less problems.