Even with 4GB of 8750, 750m & 740m are higher?
While gaming on laptop with a screen resolution of 1366x768, even 1GB graphics card is more than enough. For 1920x1080, 2GB is enough.
Video memory is never a performance index for graphics cards. The general assumption that 2gb card will be faster than the 1 GB is all wrong. So it will always be 750>740>8750.