I have a 27" ASUS PB278Q display equipped with a display port, the monitor has a resolution of 2560x1440. If I connect to my thunderbolt port using a mini displayport to displayport cable will it maintain the ultra hi-res of 2560x1440 which is what Apple claims Thunderbolt can produce?
This discussion in the Apple Support Communities says to use the Mini DisplayPort to DisplayPort Cable to get the full resolution with your monitor. That thread also tells you to avoid anything to do with HDMI which is unable to sustain such a high resolution.
Caveat: Whilst I do have a late 2012 Mac Mini, I (sadly) do not have the ASUS monitor. You may want to wait for a first hand answer from someone who owns both.
I have a 27" ASUS PB278Q connected to a late 2012 mac mini using a mini displayport to displayport cable, and I have 1920x1080 :-(
I have the same ASUS monitor and a 2012 Mac mini, but I'm running Ubuntu 15.10. I love the 2560 x 1440 resolution.
Sometimes the monitor fails to detect a signal from DisplayPort; when that happens, I have to switch to using the HDMI connection for a while before switching back to using DisplayPort.
HDMI supports resolutions above 1920*1080 just fine, just not on Mac. I have a 29 inch display with a resolution of 2560*1080 that works just fine through HDMI on my windows pc. However when I connect it to my Mac mini Mac OS X doesn't give me the option itself.
With SwitchresX I was able to set the resolution to 2560*1080 @51Hz which may not be ideal but still is perfectly fine. Since the program is only free for the first 10 days I finally settled with the less expensive mini displayport to displayport cable option.