Ive been a member on the benzo forum for 1 year now and youll see that almost nobody there has taken extremely heavy doses, it seems more of a predisposition or a certain body chemistry that some of us have that determines how well react to physical dependency (not addiction to the good feeling), or the intensity of withdrawal and time needed to recover, or any possible toxic effects.
Ive tried many of the ADs, paxil worked really well (the only one), never had a problem with anything, Adderal, but Xanax really messed me up.
"For some chronic benzodiazepine users, withdrawal can be a long, drawn-out process. A sizeable minority, perhaps 10 to 15%(3) develop a "post-withdrawal syndrome"(4), which may linger for months or even years.
IV. OTHER BRAIN CHANGES
"Since tolerance to and recovery from the cognitive changes associated" with long-term benzodiazepine use is incomplete and some neurological symptoms appear to persist indefinitely, it is difficult to explain these symptoms only in terms of slowly reversible receptor adaptations. Perhaps some receptor changes are incompletely reversible but the possibility remains that long-term benzodiazepine use can cause permanent neurological damage.
http://www.benzo.org.uk/pws04.htm
This I can say happens for sure, it happened to me and another person i know indirectly through a neighbor.