Design - for speed

Hello,
I've got the nexto problem:
In my MS SQL database I've got a table with hundreds thousands of records. In this table is field with XML content. The table has about 20 aother fields. The records represents job to do. When it is done,on the filed "Done" it gets boolean Yes. When it is done, I don't need the XML field anymore (only for backup purpose}, but other fields of the record are needed for statistics. So I'd like to know, if is better to ad one field where I would insert the packed XML (and delete it from original fled) or would be better create new table where store packed XML fild and delete it from the original field.

Thanks a lot for yout help

Andrew Sider