I suppose I wasn't clear in the original message when I wrote....

In F22 with nVidia they both worked well with native 2560x1440 resolution.

To be clearer....  In F22 running the nVidia drivers the monitor connected to HDMI was
getting 2560x1440 resolution.
Unless you have HDMI 2.0 it was 2560x1440@30 not 2560x1440@60. I don't have hardware to test if Nouveau limits resolution to whose capable of @60. From your desciption it sounds like Nouveau does that.  

Note that DisplayPort is capable of 2560x1440@60. 
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Kari Koskinen