Almost a year ago I overdosed on 20mg+ with half a bottle of vodka or so before I had a blackout. I heard that I vomited a lot and woke up in a mental ward a day later, other than that I dont remember anything.
So therefore from personal experience, take antiemetics beforehand, and just take as much as you can with lots of alcohol. I dont know what a lethal dose is, it depends on how much you weight as well, but I am kinda sure if you take like 50 mg and drink a whole bottle or two theres no going back.
Also, xanax messes up with your head a lot if you OD and survive, apart from the amnesia I had a lot of trouble focusing and thinking for the next couple days after I woke up, so just make you that you don´t if you take a lot of it.