318 MAX fuel economy builds?

Very good and I do not debate this. On the Rhoads site they have a question and answer section and they claim that valve spring pressure is not an issue because the lifters bleed down is based on engine speed and the time the bleed hole has to bleed and is lined up and able to bleed down. Since liquid does not compress I assume and that's all it is is a hypothesis bases on their statmente that the ratio and spring pressure varying to a degree of changing the way the lifters perform will be minimal and not noteworthy for my application at least.
Truly the spring seat load is the force depressing the plunger as it bleeds off, which can be anywhere from a stk HP 340 @70#, to 140# for a decent dual spring × whatever rocker ratio. Once any preload has been bled off, then it does become a function of oil pressure & orifice dimension.
As to OE VVT/VTEC etc., they are specific & are sensitive to beyond parameter changes, they assume OE spec oil viscosity & monitor oil temp & pressure to adapt the controlling OCV's or magnetic actuators. Toyota,..yes Toyota, screwed the pooch when going for the gas mileage gold w/the Camry mill, and those systems wouldn't function on the reduced viscosity as factory filled & specified. The fix, go back to 10W-30, the system just wasn't calibrated for super light weight oil.
I'm curious to see how You & the OP fare in Your individual mpg quests.