While searching for a good PWM-free 43" IPS 4k TV to use as a monitor, I stumbled upon the Acer ET430K. Microcenter sells these new for $499.
The Official Acer Certified Store on eBay is selling recertified models for $391.99 w/ Free Shipping:
43" 3840x2160 @ 60hz
IPS 10-Bit panel
5ms response time
200mm x 100mm VESA mountable
1x DP in, 1x DP out, 1x Mini DP in, 2x HDMI in, 1x 3.5mm audio out
Mine arrived today, and so far I'm impressed. There are some mixed reviews out there, with some people noticing image retention, but I haven't had any issues with it at lower (non retina-burning) brightness levels. No gaming-specific monitor specs, but IMO this thing is a steal for under $400.