Sql-server – Performance issue with xpath in SQL Server 2008

I have a table with lots of large xml-documents.

When I run xpath expressions to select data from those documents I run into a peculiar performance issue.

My query is

SELECT
p.n.value('.', 'int') AS PurchaseOrderID
,x.ProductID 
FROM XmlLoadData x
CROSS APPLY x.PayLoad.nodes('declare namespace NS="http://schemas.datacontract.org/2004/07/XmlDbPerfTest"; 
/NS:ProductAndRelated[1]/NS:Product[1]/NS:PurchaseOrderDetails[1]/NS:PurchaseOrderDetail/NS:PurchaseOrderID[1]') p(n)

The query takes 2 minutes and 8 seconds.

When I remove the [1] parts of the single occurance nodes like this:

SELECT
p.n.value('.', 'int') AS PurchaseOrderID
,x.ProductID 
FROM XmlLoadData x
CROSS APPLY x.PayLoad.nodes('declare namespace NS="http://schemas.datacontract.org/2004/07/XmlDbPerfTest"; 
/NS:ProductAndRelated/NS:Product/NS:PurchaseOrderDetails/NS:PurchaseOrderDetail/NS:PurchaseOrderID') p(n)

The execution time drops to just 18 seconds.
Since the [1]-nodes occurs just once in each parent node in the documents the results are the same except for ordering.

Actual execution plan for the first (slow) query is

and the second (faster) query is

Query 1 full screen Query 2 full screen.

As far as I can see the query with [1] does the same execution as the query without, but with the addition of some extra calculation steps to find the first item.

My question is why the second query is faster.
I would have expected the execution of the query with [1] to break early when a match was found and thus reduce the execution time instead of the opposite.
Are there any reasons why the execution does not break early with [1] and thus reduce the execution time.

This is my table

CREATE TABLE [dbo].[XmlLoadData](
    [ProductID] [int] NOT NULL,
    [PayLoad] [xml] NOT NULL,
    [Size]  AS (len(CONVERT([nvarchar](max),[PayLoad],0))),
 CONSTRAINT [PK_XmlLoadData] PRIMARY KEY CLUSTERED 
(
    [ProductID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, 
       IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, 
       ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

Edit:
Performance numbers from SQL Profiler:

Query 1:

CPU     Reads   Writes  Duration 
126251  1224892 0       129797

Query 2:

CPU     Reads   Writes  Duration 
50124   612499  0       16307