Samsung S24A650SSK (the one I have) is $50 less than the GW2750HM and it has speakers and motion/light sensor. No DAC as it does not have HDMI.
So copying your list and modifying it
GW2750HM (pros)
-built-in speakers and DAC
-HDMI input
-better response
-better native contrast (I don't believe this yet)
S27A650SSK (pros)
-better OSD (has on screen indicators where the buttons are for use in the dark and is more responsive)
-built-in speakers and motion/light sensor
-better build quality
-DisplayPort
-semi-gloss coat
-better stand (rotate + height)
-super fast start up time (I see all of my post screen and resolution changes in games are instant)
So copying your list and modifying it
GW2750HM (pros)
-built-in speakers and DAC
-HDMI input
-better response
-better native contrast (I don't believe this yet)
S27A650SSK (pros)
-better OSD (has on screen indicators where the buttons are for use in the dark and is more responsive)
-built-in speakers and motion/light sensor
-better build quality
-DisplayPort
-semi-gloss coat
-better stand (rotate + height)
-super fast start up time (I see all of my post screen and resolution changes in games are instant)