I just bought the LG ultrawide 21/9. The reseller advised me the miniDisplayport to HDMI. No way I could get the screen the way I wanted: in my case that is no split screen, just the desktop spread over the full width of the 21/9 screen without deformation. My MacBook preference display settings spitted out only 'TV' type formats. Resolution was terrible, and the whole desktop image was simply stretched to fit the 21/9 format. The topleft apple icon looked like it had been smashed by a truck. Back to the reseller, who swore that the fault was my old macbook (end 2008 model that I revamped with mavericks and 8G ram, incredible transformation by the way). But I still decided to buy a miniDisplayport to Displayport cable, the reseller looked at me the way resellers look at any stubborn, stupid and ignorant customer. My reasoning, knowing how apple does things (I worked there for 7 years) : if a mac sees HDMI, it thinks it's a TV, so it spits TV formats. If it sees a full Displayport connection, well, it thinks it's a display, and spits out display formats. And for sure, bingo, I got all the formats I wanted in Preferences, the mac automatically selected 2560x1080. Looks great.