Just for future reference, it's impossible to tell how much will be lethal for a particular person.
Some people die from extremely small amounts, and some people are able to take huge amounts and be fine. There are so many different factors that can affect what the safe dose is and what the dangerous potentially lethal dose is for an individual. It's really not a smart idea to mix benzos and alcohol, and if you are going to anyway, start with very low doses/amounts and be very careful. Don't play around with trying to find the absolute maximum you can take/drink without killing yourself.