Let me see if I can explain this. Lash adjusters are tiny hydraulic spring absorbers that have zero actuation. Well actually they do. Its called bleed down.
As the cam lobe applys pressure to the follower, the lasher begins to compress into its bleed down untill its bottomed out. The cam lobe advances more pressure finally compressing the valve and spring. Now here is the thing. Lashers have a job to do and they do their job well when being supplied the proper weighted fluid. As we know the fluid is used to control its damping rate. Since Gt exhaust lashers are designed for a heavier 5w50 oil. Why 5w50? Because of the Gt intake lasher. Its half the size of the exhaust lasher and must be able to do its job double duty. The intake port is raised needing a tiny lasher. Tiny lasher to do its job needs a heavier weight fluid, their for the Gt exhaust lasher has to be designed for the appropriate weight fluid as well. Since gt lasher bleed rate is designed for 5w50, using thinner 5w20 will alter the bleed rate. Ultimately delaying exhaust opening point.....a good thing at high rpm's. This is more of a fluid like motion that words could not put into perspective.
This would aid in low rpm ranges I would think as well as boosted cars by not letting that boost out as quick.