Thanks for the reply Terra. Kindly consider the veterans for priority whenever you get this going
From a layman's point of view I believe that the new Google Site Map Generator will play better as it does not have to crawl like the old one but as you point out the other factors offset this to some extent.
I will go ahead and uninstall the PHP site map generator and ask for a refund as we have found a free non-server based one that finds more pages for the sitemap.xml and we just edit the resulting sitemap.html in Dreamweaver.
Or we might just go ahead and install the old Google Sitemap Generator and experiment with Putty to do this.