Mystery solved. I somehow misread the index structure. It's FK, PK not the other way around, so the FK value isn't superfluous and in fact should aid the situation where mass order imports occur when we have heavy online user entered orders.

Thanks again,
---J

<snip>
>That's my issue, as well... and the one I'll be bringing up with our "guru" since the FK column doesn't seem to add anything to the uniqueness of records due to our business rules (it's a combination of PK OrderID and FK order import BatchID... but the OrderID is already guaranteed to be unique, so what does the BatchID bring to the "table" that it should be part of the clustered index?). IOW, excellent candidate for an index, but why clustered?