4K Monitors - confused over specs

Can someone tell me what the difference is between these 2 monitors, and why the price is almost double? Is it purely G-Sync or am I missing something?

Acer XB271HK (~£750) and LG 27UD68P (~£390). Both are same res, same IPS, same 60Hz, etc.

Also, when using a 3840x2160 display at lower res in games, do they perform OK at 1440p? I've always felt that 1080p would better (smoother) as it is half the res of 2160p rather than having to do all sorts of interpolations of pixels for 1440p.

They seem quite similar as you post. The 27UD68P uses an 8 bit*panel with A-FRC to give a 10 bit (1 billion) color range. If the Acer uses a real 10 bit panel, that might make it more expensive, but I*haven't been able to find whether it does or not.

I don't do much gaming, and I haven't tried non-native resolutions on my UHD monitor (Samsung U28D590D, a lowly TN monitor).