By the way, I saw the 58" at Costco and it looked phenomenal with 4K images. (far better than any 1080p LED at Costco in any size)
I did not see video. So, I could not tell how well it performed in terms of motion.
However, I own a Toshiba Regza Fully backlit Cinema 240hz and have never seen any problems with motion.
The Toshiba is supposedly 240hz and LG is 120hz. Probably not much of a difference.
The Toshiba supposedly has a quad processor and dual processor for different functions (6 CPUs).
The Toshiba is already HDMI 2.0 and ready for 4k content. Others, you have to wait for a software (firmware) upgrade.
The L9300U has local dimming with multiple zones. There is some tweaking to get this to work correctly.
I did not see the Costco price. So, can't tell you that.