Unfortunately I'm already up there. I was rx'd 5 mgs of alprazolam a day and that took the edge off. My tolerance for rec use is 20+ mgs.
What I had meant by trying the lower end of the conversion first was that if you are fine at the lower dose, then it wouldn't really benefit you to go to the higher dose just because some chart says it's about the same.
So with the .5 xanax = 10mg valium conversion, that would have your 5mg xanax equal to around 100mg of valium.
Now with the other conversion chart that says .5 xanax = 5mg valium, your 5mg xanax would be around 50mg of valium.
My point being, there is no need to be on 50 more mg of valium if you are fine at 50mg. My bet is that you would be fine somewhere between the two, at around 70mg. I don't know if you ever plan on tapering or not, but it would be a lot easier tapering down from 50 or 70mg than it would from 100mg. I am glad that my doctor used the .5 xanax = 5mg valium conversion, otherwise the taper would have been twice as long for no reason.
Even if you don't intend on getting off of benzos, you are better off being on a lower dose. When I tapered, once I stabilized at the lower dose for a few weeks before lowering it again, my anxiety was the same as it was at higher doses. In other words, I felt the same, if not better, on 4mg of valium than I did on 4mg of xanax, and also on each lower dose of valium I felt pretty much the same until I got below 2mg. A lot of people being prescribed benzos don't have the chance to realize that their anxiety has gotten better because the drugs screw with them, and the withdrawals that start in between doses are usually mistaken for regular anxiety, which make you think that you really still need those high doses of benzos.
Edit: If your doctor dropped you from 5mg xanax to 15mg of valium, that is way too big of a drop. I'm all for trying to get down to lower doses, but that is too extreme.