[Zope] Timeouts from overseas?

I have an international customer who claims that their European offices have difficulty receiving pages (roughly 50% failure rate) from our Zope server here in the US while at the same time they have no trouble receiving pages from our apache server. Both servers run on the same physical machine, and the hostnames are served from the same DNS zone. It would seem the only variable is the http server software - zope vs. apache. Just to complete the picture, they say that their US offices have no difficulty receiving pages from any of our servers. Is there some timeout value that I might try adjusting? I know I can serve the Zope content through apache/PCGI. I'd rather not.