http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=c03294528&lang=en&cc=us&taskId=101&contentType=SupportFAQ&prodSeriesId=5187028&prodTypeId=12454 shows a similar PC so just like the other discussion the 5450 would be my choice here.
As to the switch, I move the monitor video cable to the new card.
Bob

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