I've read ridiculous amounts of ZDDP can cause galling, so WAY too much isn't good I suspect. I like Redline multiweight oils, but for the price, Valvoline VR1 is suuposed to have the right amount of ZDDP for not much money.
Redline oils are great. I agree. That is the only exotic brand I like. Redline does what it's supposed to, unlike some other exotic brands.
However, Mobil One is just as good IMO and costs way less. Airlines use Mobil One is their passenger jets and the military uses it in their fighters. Those are the most expensive machines you can think of, and the most lives at stake of any application I can think of, and they use Mobil One.
If you want something that costs a lot less than Mobil One or Valvoline, then Chevron Delo 5/40 is it. The Delo is excellent stuff and very low cost for a gallon of it.
My only concern with the Delo 5/40 is that it has 1260 ZDDP ppm which I think is to much for cats newer than 2000. Other than my concern about newer cats, I think the Delo 5/40 shares the "best lubrication" spot with Mobil One 5/40 for best lubrication for a 4L engine.
But the thing I like about Mobil One 5/40 is that it gives that same level of "best lubrication" without threatening newer model years of cats. So that's why I prefer the Mobil One 5/40 for my 2006 4L.
If I had a 4L that was 2000 or older (not worried about cat), then I'd prefer the Chevron Delo 5/40 full synthetic because it gives just as good lubrication as the Mobil One 5/40 full synthetic, and the Delo 5/40 is very affordable
(costing only as much as typical over the counter conventional oils).
The only problem with Chevron's Delo oils (Delo is Chevron's heavy duty oils for trucks) might availability outside the West Coast. Delo 5/40 is NOT sold at auto stores, at least not that I've seen. Delo oils are typically sold at trucking supply places. Also, Chevron specialty products like Delo are widely available (and inexpensive) on the West Coast, but are hard to find on the East Coast (and might cost more on the East Coast).
The reason I also recommended Chevron Supreme 5/40 full synthetic (an over the counter consumer oil for new model high performance muscle cars) is that it's lubrication is almost as good as the Delo 5/40 and Mobil One 5/40, but the Supreme's 5/40 is VERY CAT SAFE even for current model years cats and offers above average lubrication. The cost of the Supreme 5/40 is the same as Mobil One, at least in my local area. So the only reason to use Chevron Supreme 5/40 is to give cats max protection and engine good lube. But the Chevron Delo 5/40 and Mobil One 5/40 give the best lube.
The Mobil One 5/40 is the only option that gives best lube and good cat protection too, IMO. That's why I prefer it. Well, Redline is just as good as Mobil One, but not better. Redline costs way more though.
However, for anyone wanting maximum overkill amounts of ZDDP (against my advice for cats), you can have your max overkill amount of ZDDP very affordably, without having to buy additives or expensive exotic brands of oil. If you want max overkill amount of ZDDP in a full synthetic, then buy Shell Rotella 5/40 full synthetic because it has 1550 ppm of ZDDP. Great for lubrication, but way to much for any year of cat, IMO.
It's unnecessary to have that much ZDDP for lubrication because a good synthetic oil only needs 1000 to 1150 ppm to give great lubrication. Newer model years of 4L cats can handle up to 1100 ppm. Older model years of 4L cats can handle up to 1200 ppm just fine (and probably can handle Chevron Delo's 1260 ppm OK too).
None of the less, if you want maximum ZDDP, Shell Rotella 5/40 offers that, along with a great base oil, and at a very low cost. Shell Rotella 5/40 is a low cost as Chevron Delo 5/40 because they are competing for the same turbo diesel light truck market.