It's hard to say, because alcohol affects other people differently depending on body composition, tolerance, type of alcoholic beverage and so on, but for me personally, my SI is at its lowest (while still being "functional" and not nauseous or significantly more stupid than usual) when I'm roughly between being tipsy and drunk. Like, that warmness over the body and floaty feeling in the head type of thing, but still not tripping over my own feet and twerking against inanimate objects.
Maybe you could do a little experiment to gauge how you feel after a certain amount/type of drink(s) and make some notes on what you drank and how much within a certain period of time, so that you're not just winging it on the spot IF you decide to go through with it? The decision to die is obviously a serious one (and not one that I encourage anybody to do, for the record – it's about personal choice and really understanding what you're doing and the consequences thereof), and not something that should be "winged" at any point, and in general it's always good to really know what you're getting into before you get into it, if and whenever possible, even when it comes to the nitty grittys. I'm sure you're already well-aware of this, but I specifically mention it anyway, just to be safe.
Also, I'm not judging you, but it just sucks so bad that people – who are already (clearly) in enough pain as it is – have to resort to such grisly methods when we have the medical knowledge and resources that could allow people the option to go peacefully. What a world we live in. Hurts my heart. I'm so truly sorry that you're hurting so much.
