Well done, AA, and Thanks for your Thanks.
Your D-Link.au site gives more info than the .uk site about Power outputs etc. The 650 and 520 are stated to be 15dBm. (Relative to what they don't say). They chatter away happily (Peer to Peer/ad-hoc) though thick walls and floors with "Excellent Signal Strength" in the Taskbar.
When I change the setup to "infrastructure" on the ADSL Modem/Router (stated to be 14dBm), the signal strength drops right off and contact through the 650 (for PPRuNing etc) is intermittent. The Router (604+) and the 520 in the Desktop are almost co-located. When I get the time, I too will be on the 'phone to support.