After a few minutes of playing the fps drop from ~150 to ~50 and after 20 minutes it becomes unplayable with unstable ~25, which can be fixed by restarting the game. People with better specs like GTX 1070 are able to play for around 40 minutes.
This kind of heavy performace drop happens only on nvidia GPUs and i was able to maintain stable 40 fps on Intel HD 4000.
This also doesnt happen with Windows + wined3d + nvidia GPU
System: Host: Dell Kernel: 4.10.8-1-zen x86_64 (64 bit gcc: 6.3.1) Desktop: KDE Plasma 5.9.4 (Qt 5.8.0)
Distro: Arch Linux
Machine: Device: desktop System: Dell product: OptiPlex 755
Mobo: Dell model: 0GM819 BIOS: Dell v: A22 date: 06/11/2012
CPU: Quad core Intel Core2 Quad Q9650 (-MCP-) cache: 6144 KB
flags: (lm nx sse sse2 sse3 sse4_1 ssse3 vmx) bmips: 23947
clock speeds: max: 3000 MHz 1: 2000 MHz 2: 2000 MHz 3: 2000 MHz 4: 2000 MHz
Graphics: Card: NVIDIA GM107 [GeForce GTX 750 Ti] bus-ID: 01:00.0
Display Server: X.Org 1.19.3 drivers: nvidia (unloaded: modesetting)
Resolution: 1920x1080@60.00hz, 1920x1200@59.95hz
GLX Renderer: GeForce GTX 750 Ti/PCIe/SSE2 GLX Version: 4.5.0 NVIDIA 381.09 Direct Rendering: Yes
Network: Card: Intel 82566DM-2 Gigabit Network Connection driver: e1000e v: 3.2.6-k port: ecc0 bus-ID: 00:19.0
IF: enp0s25 state: up speed: 100 Mbps duplex: full mac: 00:21:9b:2f:7e:bc
Drives: HDD Total Size: 3250.7GB (5.8% used)
ID-1: model: Crucial_CT250MX2
ID-2: model: ST3000DM001
Info: Processes: 215 Uptime: 3 days Memory: 2988.7/7859.6MB Init: systemd Gcc sys: 6.3.1
Client: Shell (zsh 5.3.1) inxi: 2.3.8