Hmmm.... this has no put me in semi-catatonic states at ROA oral 500mg (after building what I though was a substantial tolerance). The second time I really have zero memory of being that screwed up, but people around me can confirm. The thing is, it would be worthwhile if I can remember anything useful from a hole-like experience or whatever, but I can't remember anything at all.
NB this is a stupidly high dose to take, even after using semi-regularly for 1 1/2 years. I am giving this chemical a wide berth. Up to 250mg it doesn't seem to give me much at all, even 300mg, but when I start to push it higher all hell breaks lose. Unrealiable, inconsistent dose-increase response curve, more and more stories of people either blacking out or having horrible times. I think my love affair with this chem may well and truly be coming to an end. I like to be able to recall something from my dissociative experiences, and it concerns me when I can't remember anything at all.
Let me get that straight. The highest dose you tried was 300mg, with an unknown tolerance at the time. Now you try almost twice the dose and blame the dose response curve for blacking out? This isn't coke or speed where you can just take 50 doses and still be fine.
I am not sure what your experience with other dissociatives is, but let me give you an idea how the most popular one behaves at varying dosage levels. There is a sweet spot which lies between 75 and 200mg IV for most people. If I go as little as 20% above that sweet spot it results in a total blackout. Compared to that, 2-MeO-Diphetidine is a very forgiving dissociative, it's a lot like PCP in this respect.
The real issue is that people want to treat this like a psychedelic or stimulant. If throughout 18 months you have not been able to take the time and slowly increment from those 300mg that didn't do much, this drug just isn't for you.
Oh and I personally found my sweet spot to be around 400mg orally, 250mg IV. Complete and utter insanity, delusions of having died, being possessed by demons, I was even blessed with my first near death experience in 17 years of drug use. THe only thing all these experiences had in common was that each and every time they had me scared shitless - completely rapt with existential fears, a primal fear as honest and brutal as fear comes. On the plus they gave me a taste of what life would be like as a god.

Much less pleasant than pretty much any other glutamatergic dissociative I've tried, but reaching way down to the core of my soul, surely deeoer than ketamine or pcp have ever gone - and I've done a lot of pcp and ketamine.
EDIT: Sorry if I sound like an asshole there NiceEnough, but I assume you know well enough that what you did didn't promise to be successful to begin with. I assume it was a 'spontaneous thing'. I am not here to convince you of the wonders 2-MeO-Diphetidine can introduce you to, but I still don't think you've done what you could have done in your attempts to uncover the potential of this substance.