That monitor seems overpriced, but I am not familiar with European price points.
Is there any way of just spending the money on an upgrade to your PC? Components are relatively cheap and easy to install compared to purchasing a new rig. A processor and RAM upgrade would likely increase your performance for cheap, an SSD would help with load times, and a decent video card would help render graphics more smoothly. I currently have my PC wired into a 40" TV in my room. I find the lag everyone keeps complaining about unnoticeable (please don't ruin that for me by pointing out something I can't unsee). I am super happy with my setup.
The only reason I would get a PS4 is if the majority of my friends had one, or if I really liked anime games from japan and other exclusives etc.
From what I understood my motherboard wouldn't allow me these kinds of changes.
Also I don't know anything about changing PC components. My current PC was assembled by the website who sold it to me.