That is really it end of story
read this, the most important feature of any oil is always viscosity, and 5w30 is considered a thin oil anyway. It is just that 20 weights are super thin. As to answer your question why redline, it is because it is ester/pao based and that provides performance in the extreme conditions that cannot be matched with group 3 oil. This is specifically why it is proven a good choice under ticking conditions, COLD CLIMATES, and towing etc.
However, the question remains always is that extra cost worth it in the specific application of a gas engine, most people say it is not. There are many things they put into group 3 oils such as Vii's and Detergents and a list of other additives that make up for what happens naturally with esters. The argument for esters/pao base is much stronger for other applications like the gears and tranny, thus is why the new tranny fluid is specifically PAO based.
If you are happy with what you are using, follow the if it aint broke don't fix it crowd, maybe consider same brand just go to 30 weight. Learn about how UOA's work if you want to take the argument further. With the newest spec ilsac gf-6 which Amsoil currently has I believe and most oils do not yet, all oils will be very similar in additive package. If you want something radically different like Redline, you have to leave the API oils or maybe look at GtL base oils.
The Amsoil formulas are very new and dramatically different then they were a couple months ago, it will be a while before we see a lot of uoa's and see how it is going. M1 had made the switch to a GF-6 friendly formula many years ago, I believe the only company to do so, other then M1 every group 3 oil selling company will have new formulas that nobody can say for sure it is or isn't good for any application. It is an unknown.
There has been a lot of debate and trouble with the GF-6 spec, the goal of providing a lspi friendly oil that also meets CAFE standards is proving to be a hard sell because these formulas are leading to excessive wear. This is why they keep pushing the GF-6 spec back, it is a very large quagmire for the oil industry.
Read here and decide if you want to run an oil that was built to meet GF-6 in your hemi.
from link
Two tests have proven particularly challenging to complete. The Sequence IVB test evaluates a lubricant’s ability to prevent wear in modern valve trains. The Sequence VH test evaluates a lubricant’s ability to prevent engine deposit buildup, more commonly known as “sludge and varnish.”
Well it is apparent that the "wear" protection will never be achieved in comparison to the current GF-5 spec. It is a bunch of garbage to think they will achieve this, unless they embrace esters and pao's which is not likely. There is only so much you are going to get out of group 3 oil. Like Clint says, you just need to know your limitations. They will meet every other goal, low additives to help DI turbo's and thinner oils to to give better fuel economy in a lab, but these will come at a cost and the cost will be the oils will be less effective at preventing wear in a long oil change interval. Someday someone will invent a self healing Vii and all of these things will be possible, but until then there is a cost for going to low additive -thinner oils.
A lot of this challenge can be avoided by simply going to 30 weight and not worrying about fuel economy. Running 20 weight gf-6 is a risk, that is why the spec keeps getting pushed back.
Did you want a less detailed answer, my bad
