I prefer the smallest one (it says "looks like 1680 x 1050") -- because I have a bunch of apps running all at the same time, and it helps to have them all viewable on the same space.
Try opening up more tabs in safari, see if that matters...or try a larger / more colorful PDF, like a restaurant menu. But anyway...
No. Apple clearly states that the HDMI output is limited to 24 or 30 Hz.
This includes the 15" retina with the 750M!
And this is a limitation of HDMI itself -- HDMI 2.0 was just late to the game, so Haswell shipped without it.
All these 2013 macs, all of them, are stuck with HDMI 1.4.
Also, no GPUs have HDMI 2.0 yet as far as I know -- none that are shipping anyway.
So in order to drive 4K displays at this point in time at 60 Hz, you need multi stream display port (display port 1.2), which uses two 1080p streams and combines them into one...again, not supported in Mavericks yet. It's expected that when the "new mac pro" launches, this will be fixed...but I'm not holding my breath.
And yes, you'll see mouse lag running a 4K display at 30 Hz.
The "gold standard" for computing \ scrolling \ screen refresh rate has always been 60 FPS or higher. Some people say you really can't notice anything higher than 60 FPS, but whatever. 30 FPS is half of what you're normally used to....it won't be pretty 😝