After strugling some time with the profiler (my
debugfile never showed
any content) I tried the Eaccelerator knowing this might (not) be the
answer. But it was. It increased the speed significantly, whatever the
cause was. Thanks!
You're probably just hiding the problem, though. Eaccelerator will
just speed up viewing pages that have already been parsed, it won't
speed up viewing pages for the first time (and that's first time for
each logged in user, I expect, so the difference may be minimal if you
test with other accounts).