Poor performance when mapping XML to Excel

[findus2007]

Hi all,
I have got an XML file, which I produced by serializing an object, which
represents my data I want to be able to work with in Excel (Office 2003,
Interop, no VSTO).
When I do the mapping by looping over different branches in my XML and
calling:

cell.XPath.SetValue(map, myXPath, myNamespace, false);

everything works fine. But for large objects I noticed, that this mapping
time arises with each cell a little bit. For example with every 300 cells the
time seems to be multiplied by 2.

Is this behaviour correct? What can be done to overcome this issue?

I know, I can switch to column based mapping. But it has a lot of assumptions
(data as lists,..) which I cannot do with my multidimensional data.

Any help will be highly appreciated.
Thanks