I own an iMac Retina 5K 27-inch, Late 2014. I use it in a bit of an unorthodox way. I use it as the only display at my "standing desk", but I also have a sitting desk about 8 feet away. I currently feed two external monitors over to the sitting desk. The two 24" monitors there are both 1080p. I want to improve the readability of the text on my sitting desk monitors. I believe this model of iMac can drive two 2560 x 1440 displays or one 4K display. Will upgrading to two 25" 2560 x 1440 displays help? How about two 4K monitors? Will doing so lower the refresh rate? Due to my average (old) eyesight, I believe I'd only want to display the external monitors at 2560x1440 anyway. Thanks for any advice you can offer!