I once took an entire bottle of clonazepam (90 pills at 3 mg/pill) and topped it off with A LOT of alcohol. I had a good night's sleep and was pretty calm for the rest of the week - but it did not kill me. In retrospect I really should have researched it first. It was such a waste of some good meds.
A quick google (not sure of the source of the info for these results) indicates that the LD50 (or the dose at which half of the population tested died after administration of clonazepam and it is important to note that this was half the population not all) was reported as follows: "Some oral LD50 values documented are >4000 mg/kg for the mouse model, >4000 mg/kg for the adult rat model, and >2000 mg/kg for the rabbit model."
In essence, these results show that it would take a HUGE amount and even then there is no guarantee that it would work as the LD50 is so variable and half of the animals survived even at these high doses. Not to mention these are animal models, so at best it would be a guess if the LD50 is the same in humans.
All in all, benzos are not really a viable option. There are other factors that would impact this such as the fact that tolerance can build up with these meds over time, so that it takes more and more of the med to work.
Not really a viable method and I would be careful because high doses may cause damage or adverse outcomes in other ways.