Opiates can be extremely personal, meaning that some opiates are effective for some, and not effective for others. I too have found that hydrocodone doesn't have really any effect on me, and oxy's tend to have a little more, but I would never use them for a high as they barely do much for my pain, but again this is very individual. I have heard alot of people who say they love hydro's over oxy's and vise versa.
As for benzo's 2c-goinsane is spot on. Benzo's should never be used for a long period of time as addiction is extremely high with these and the longer you take them, the less effective they become and you always find that you have to 1 up them. If you have taken them for a long time, withdraw is a very real, very dangerous ordeal. For the most part the only safe way to come off of them is through a very controlled taper. The withdraw from benzo's are very much the same as alcohol withdraw, which is why when withdrawing from alcohol, you will be prescribed a benzo taper. Another serious effect of benzo withdraw is severe depression / anxiety. The scary side to this is that sometimes well after the withdraw has seemed to be over, all symptoms gone, and you are off the drug, I have heard many people (including someone who I was in a rehab program with) tend to get really severe panic / anxiety attacks well after all activity with the drug is out of their systems. The person I was in rehab with had been off Xanax for almost 2 months and had a panic attach completely out of the blue so bad she was hospitalized for it. This is something you really want to avoid at all costs.
I know you only planning the xanax to help you out and not take it for an extended period, however, since it was bought out, I felt it pertinent to bring up these points.
Cheers!