Macbook pro 2014 and 4k display

Hello everyone, I know that's hackintosh forum but i think only your magic spells can work something out.
I own a macbook pro 13 2014, and few days ago i bought a 4k display dell p2715q and everyhing works great BUT only when im on 3840 × 2160 resolution, with no scailing. The problem is that everything is wayyy to small so i bumped up scailing to 2560x1440 and it looked good but performance were not so great, everything slowed down dramaticly, so i clicked menu button on dell and saw that display was reciving not 2560x1400 but 3840 × 2160 resolution and its so slow becouse of that ****ty scailing. So i grabed "Desktop Menu" app (tried SwitchResX too) and i set 2560x1400 in app and yes, display was reciving exactly this resolution and it was smooth but! fonts and well, everything was blurred. Then i noticed something else, when i switched scailing ( in osx preferences, not in any 3rd party app) to something around 1280x768, display was reciving 2560x1400 and i saw 1280x768 and it was quite sharp. So, is it possible to maby add an option to scailing options where i would get full hd on screen and 2560x1440 would be send to display? (Nope, there is'nt that specific option). Basicly, I want full hd or 2560x1440 resolution thats sharp and won't decrease performance.

Oh and there's something weird, some resolutions have "low resolution" label, i don't know that that means

I recommend you look for an answer in the MacRumor's MacBook Pro forum section > http://forums.macrumors.com/forums/macbook-pro.90/. If you don't find an answer, open a thread stating your problem.

Good Luck!