The cheapest 4k Dell monitor is €494.75 off amazon.co.uk. https://www.amazon.co.uk/Dell-P2415Q-23-8-Inch-Ultra-Monitor/dp/B00R420WNM/ref=sr_1_1?ie=UTF8&qid=1463910292&sr=8-1&keywords=Dell+Ultra+HD+4K+Monitor+P2415Q
same Resolution at 3840 x 2160
Dell is 6ms response time compared to 1ms on the AOC monitor. (Gray to Gray)
The refresh rate is the same at 60Hz.
The connectors on the DEll are Displayport 1.2 in, Mini displayport, Displayport out (for daisy chaining, HDMI, Speacker line out, 4 port usb 3.0 hub
The connectors on the AOC are Displayport 1.2, HDMI 2.0, DVI-D, VGA
Contrast ratio is the same at 1000 to 1 (typical)
The Dell and Aoc warranty is 3 Year guarantee
The screen size for the Dell is 24"
The screen size for the AOC is 28"
Personally I would pick the AOC because it's cheaper, bigger and has a faster response time than the dell. while you have less connectivity without a usb 3 hub, no mini display port or speaker line out I think it's worth the price difference and performance