You can run SET STATISTICS IO ON before your change, execute the query and review the results in the messages tab. Then run DBCC FREEPROCCACHE and DBCC DROPCLEANBUFFERS to clear the proc cache make your changes and run the query and review the results in the messages tab again. You can also compare the estimated subtree cost of the execution plan before and after the changes in SSMS.

NOTE - Do this in a NON PRODUCTION environment, running DBCC FREEPROCCACHE or DBCC DROPCLEANBUFFERS in production will have performance implications.

Chris