It's been a while this nice subject 240Hz monitor is around, and its users found an annoying bug in its firmware.
In its default 240hz mode with most Nvidia GPU's (which are most common gaming GPUs), monitor's picture heavily stutters in motion.
I found (and many other users confirmed) that the actual problem relies to the fact that actual refreshrate in 240hz mode is 239,759Hz. If user with any resolution-editing utility, such as Custom Resolution Utility from ToastyX (CRU.exe) changes timings to change actual refreshrate from 239,759 to 239,760 the monitor runs fine.
But it is very annoying and disappointing to new users, that in it's advertised and supported 240hz mode the motion picture stutters, if user does not fix it manually via CRU.exe
I beleive LG should fix it via a user-friendly firmware update with OnScreen Control software, the way firmware update was released to 34GK950F, and subject 27GK750F-B also has USB connectivity and USB cable provided.
There is my thread at blurbusters.com, check out the first TLDR post, it has actual iformation about currently found 27GK750F-B flaws.
It is also found that 27GK750F-B has a bit higher input lag then most other 240hz monitors, but 34GK950F mentioned above had the same problem and luckily it was fixed by a firmware update released by LG.
I ask this community managers to forward this information to LG monitors tech dept.
The problems are real and it is in LG's possibilities to solve them for their users. We request the user-applicable firmware update to 27GK750F-B to fix its current issues.