vibrancy3
Bluelighter
I have done mxe a few times, i dont diss it. but i do prefer kay 
I think the original post is inaccurate in that it states MXE has a hangover that can last days? Really? I don't find that the case at all. MXE to me lasts initially 4 to 5 hours, with a come down of an addition 4 to 5 hours. It's a lengthy high for sure.
You could mention texture... Ketamine varies a bit, usually crystalline but I never encountered crystal MXE, it was always a strange behaving, relatively fine powder. Both have been generally white.
I read somewhere that after repeated exposure ketamine becomes a more serotonergic relative to dopaminergic, which might explain it
Plus you can't really overdose on just Ketamine.
But MXE....
While I know you mean "Overdose" in the sense of a fatal overdose, I would still say its easy to overdose on Ketamine and put yourself in to an unwanted K-hole.
In fact, I'll go so far to say I'd rather overdose on MXE as oppose to Ketamine. MXE in my experience, the worst that happens is a huge rise in blood pressure and vasoconstriction where as Ketamine makes me extremely sick, vomiting and extremely disoriented.
I wouldn't say it's easy to accidentally hole. I wouldn't say snorting 150mgs is accidental, and if you're redosing a lot than it's your own fault for not expecting it.
And your reaction to a hole is unique to anything I've heard/seen. I've never seen someone consistently get sick off ketamine.
I've updated the OP based on responses here. This will be a work in progress.
If someone who has MXE on them wouldn't mind burning a very tiny portion of it on tinfoil and letting me know the colour it turns, that would be great. Ketamine burns to an oily red colour but I'm not sure about MXE.
If they burn differently then this could be a great method of identification.
Colour:
Ketamine - white
MXE - white, or off white-tan