Are the 2Gb cards going to run 2560x1440 in games without issues? From reading elsewhere on here, when trying to game at that res the 4Gb cards seem to be recommended.
HardOCP are good at testing modern games at high resolutions such as that, such as this Gigabyte GTX670 review - http://www.hardocp.com/article/2012/07/25/gigabyte_geforce_gtx_670_oc_video_card_review/1