I would take the acer x34 in a heartbeat..
It's so immersive when play with..
Unless your strictly a competitive cs:go player, go for the x34
100hz vs 60hz is definitly noticable
The only problem I can think of is that not all games support the resolution and you will see black bars, but most...
Just like @UrbanZyrx said
Also here is a build including os, mouse, and keyboard and monitor:
PCPartPicker part list / Price breakdown by merchant
CPU: Intel Core i5-6600K 3.5GHz Quad-Core Processor ($230.99 @ SuperBiiz)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU...
It has 4 threads, so it's a semi-quadcore, and your budget won't allow it, besides you don't need it, if you can pay a little bit more get an msi h170 motherboard..