hiiii. I tried slitting my throat and failed miserably, it is very hard for me to beat SI, I don't know so much about statistics, but it's not a much used method, for it being so invasive, I would love to have the guts though, cause it seems so fitting for a person like me, but I digress.
Not super used method, you can find psychology papers on attempts and case studies of few people who succeded. But in theory if you manage to hit the artery, which should be easier trying to slit than pierce, the probability of you dying it pretty high. Although it can vary from people to people, because of blood pressure, amount of blood in the body etc. Also again if you miss it's going to hurt like hell and probably won't kill you or if you only nick it it will bleed significantly less and take waay longer which give you a chance to be saved. I recomend you do some research of your own, google scholar will have stuff