Please post the actual execution plans (not estimated) as .sqlplan files for each scenario.  If you're inserting 2000 rows into @p3 and then passing that as the argument for @BusinessObjectDataGuids then that's a red flag - there are no statistics on table variables and so the query optimizer will just assume there is one row in the table.  (That number may have changed in a more recent version - I'm not sure).

John