I'm a freelance web designer who's starting to get more into responsive website design and design for retina and there are some things that I'm not entirely clear on when it comes to setting up PSDs, particularly with regard to screen size and resolution. I've been mostly working with already designed PSDs (just helping out by updating their already designed pages) - but as I'm working on more responsive projects I'm finding that each project seems to be different in that some of them are designed at a really high dpi and screen size while others are just a standard 72 dpi ( and I'm presuming are just being saved out / sized up for the developer at 2x (200%)?) Could someone settle this for me once and for and tell me what the best and most current / correct dimensions AND dpi to set my PSDs up to? Any help would be super appreciated! Thank you!