Looking into it, Alprazolam and Diazepam (Xanax and Valium) are more toxic than other benzos. I saw a paper on it and it said they had reported 60 deaths from self poisoning. It said the average overdose they treated in urgent care had 23x the daily dose. I'm guessing that's like 230mg in the blood based on 10mg daily. I don't know the real scientific answer, but based on the rate of breathing I think 300mg xanax + a blood alcohol of at least .35 preferably .40. That could work, but I'm very unsure about it. (sorry im high)
od on benzo is easy, but od ≠ lethal.
The stats you gave are probably not wrong tho,
Usually, benzo od are due to co-ingestion, most commonly opioids. the problem with benzo od is that theyre not what kill you, you usually die from indirect accidents: choking on your vomit, losing consciousness on a pillow and suffocating, falling and hitting your head, etc. Theres no LD50 for any benzo in humans yet since theres so few "true" benzo od (without any co-ingestion) and LD50 is an average. The LD50 in rats for alprazolam (xan) is in the ~300-3000mg range depending on where you look, alprazolam has the lowest LD50 (rats) of the most common benzos, most are in the 1000-10000mg range.
The reason as to why you can get toxicity from like 50mg xan but need 3000mg to die is that benzos act on GABA receptors and their toxicity is mostly due to that. For comparaison, alcohol also acts on GABA receptors but unlike benzos it has 2 extra ways to be harmful: 1. liver damage 2. toxic metabolites (acetaldehyde). Benzos dont have that.