I bought a Dell U2713HM because it was highly rated and had 2560×1440 resolution, but, after learning that the HDMI connection only provides 1980×1080, I purchased from Apple their Thunderbolt to DVI connector and tried that. Still 1980×1080. I've now ordered a mini-DisplayPort-to-DisplayPort connector and am praying that I get the full resolution that way, but I've seen a number of user group comments that you need a completely separate (over $100) Thunderbolt data (not display) interface to get the full resolution. If that's true, I'm returning the Dell. I've also seen people say you need to reset the PRAM and SMC settings, but I've tried doing that (I think it worked) but nothing changed.
HELP!
Best Answer
get a Mini DisplayPort / Thunderbolt to DisplayPort Cable $17.99 or less, thats what i did works fine, although photoshop still displays non retina so have to scale to 50% which is a pain.