Andrew,
With this, your prefix is going to the same as your sysroot. I can't imagine that this is what you really want. The prefix is supposed to be where your cross- toolchain gets installed, the sysroot, is where you put the target headers and libraries.
could you be more specific with your cricism?I tried setting --with-sysroot to various values, or even not set it - all of these result in the gcc failing to compile..
Akos