I'm a little confused about the resolutions of the iMac 21.5 inch compared the iMac 27 inch. In terms of watching HD content, which is better, as one is 1080p so it is perfectly formatted for this type of content but the other is higher (2560 by 1440 pixels), will this mean it is better because there are more pixels or worse because it is a different size? I'm a little confused about this. Also is it possible to change the resolution to 1920x1080 on the 27 inch? What will this do exactly? If I were to apply a 1920 x 1080 wallpaper for example to the 27 inch iMac will this look better/worse? Sorry if this is a stupid question but I am just generally very confused about this subject. Thanks, Alex.