Uwe, do you have a test showing that creating a Clustered Index wouldn't improve the execution plan?

Depends on the instance. Environments where one or more dbs are created for each customer, for example, I'll adjust model so that it works well for the application(s) involved. Sometimes...

I ended up moving the catalog and index to a different disc in order to ease the i/o load. It's been populating without problems since.

Thanks for the reply.