The Xara guys are on the case and they inform me that the speed problems indicated by web hoster #1 would make only a few milliseconds difference. They suggest it is a web hosting problem.

As I have the same site running on web hoster #2 this would support this idea.

I'm now loading the site to two different web hosters until web hoster #1 fixes its servers (or whatever). Not satisfactory but at least people should be able to find my site somewhere.