lardman's question about whether you really need the Xscale optimizations is a valid question that any developer should consider. It depends on what you are attempting to do with your software.
I've had a comparison between GCC optimizations on my zaurus web page for quite some time. I added another page last night which compares the SL-5600 standard and overclocked kernels with the SL-6000. The comparisons use nBench and can be found here
. You should look at the nbench-armv4, nbench-armv5te, nbench-cpu-xscale and nbench-tune-xscale tables. The results vary, but xscale opimizations usually are the best.
I guess I should mention on my web page that my SL-5600 has the PXA-250, since there are some SL-5600s with the PXA-255.