if you have 2 laptops to choose from in the same store, see if the salesperson will let you run a comparison, provided the machines have internet access
go to "can you run it" and use a recent game with moderate requirements and see how they compair with the "benchmark" game
http://www.systemrequirementslab.com/CYRI/intro.aspx
since the thingie they do to the computers needs to download something to run you will have to get the salesperson to help you, when it finishes and shows the report it gives a fairly decent list of things to compair even i am capable of understanding