Xanax XR doesn't last nearly as long as it is plugged to. I was expecting to take 1 pill a day and ended up taking two and having rebound anxiety, so I quit and went back to regular and that has helped me a lot. I wouldn't spend the extra money on it it possible. Vallium definitely lasts longer than Xanax, but also causes more drowsiness. It is one of the trade-offs involved with the Benzo's. If you do a search for "Benzodiazepen comparison chart" or something to that effect, you will find all the Benzo's in a list with there half-life and other valuable info.