We can't divide Wales, it's too much. Ordovices controlled much more of Wales than Silures, and they owned Mona, which is too important to miss on the map.
"The Siluri were considered to be more powerful than the Ordovices" - by whom, and in what context? They have resisted Romans a bit longer, but that's all I could find...
Perhaps this province should simply have the name of 'Wales' in some ancient tongue, if we can find source that there was a common name for the area used in 200-300 BC.

BTW, does anybody have more on Pytheas travels than what can be found on the web?