In the past few days or so, Ive read many members saying that 400-600mg of mescaline is "very managable" or "not too intense" or "easily navigable".

I need some clarification here on this verbiage. Is it "easily navigable, etc" for someone who has been taking psychedelics for 10 years and is unknowingly downplaying the effects that the drug actually has just because theyre used to it? Or is a 400-600mg dose gonna ego death the crap out of someone whereas if youre sitting on a bench, you become the bench and realize that the bench is the universe within its universally universal self?

Im a blank slate with the exception of spice. Never done shrooms (will soon), never done lsd (dont plan on it) and have yet to take the mesc hcl I have, which I only have a 300mg dose that will be split between a friend and I (yes, I know its not a lot but Im not down with gobbling up half a gram just for giggles and I want to give it a whirl so I can incrementally bump dosage for the next time I extract)

But, with that said, as the blank slate with no prior experience as I mentioned, if I took 500-600mg, would it be like the 5g-10g cubensis reports Ive read where the self gets shredded for 6+ hours? The lack of intensity every one seems to be describing, Im just trying to figure out if its easygoing for those with lengthy experience or if it REALLY is a much softer, navigable experience with very little potential for losing your head, you can function relatively normally, go for a walk thru the forest, converse with friends all while immersed in the beautiful healing nature of mesc etc, or not at all?

^^^ Exactly that

Mescaline dosage breaks down pretty much this way for me:
0-75 mg: elevated mood, comfortable stimulation, slight empathic effects
75-150 mg: strong mood lift/euphoria, unmistakable stimulation, pronounced empathic effect
150-300 mg: "Rolling", Strong empathic effects and stimulation similar to a light to moderate dose of MDMA (say 50-75mg), threshold psychedelic effects.
300-500 mg: Psychedelic effects, mind wobbling, oev's, bliss and euphoria, similar to taking 1-2g cubensis or 100-200ug LSD easily manageable yet actively psychedelic dose.
500-750 mg: Strong psychedelic effects on par with 2-3g cubensis or 200-300ug of LSD. You may find yourself needing to lay down and experiencing geometric cev's during the peak.
750mg-1g+: Fully psychedelic dose, oobes, visionary/dreaming states, inward focus, laying down, this is the dose where you will stop being able to actively engage the outside world for many hours.

Note individual sensitivities differ, your mileage may vary.

Now THAT is a spectacular answer, and honestly exactly what I could have hoped for, how you compared it to mushroom/lsd doses. Thank you so much for a wonderfully detailed response.