Need help to built stationary computer for playing Battlefield 4 and similar games?

[Adar]

1. Why are you upgrading? Play Battlefield 4 and similar games with a much younger brother. I still play Medieval Total War II but now I got a brother who is growing up and really want to play against me.
2. What is your budget?
   8000SEK preferably cheaper. Already got keyboard and screens but advice for upgrades are also welcome.
3. Where do you live?
   Sweden, Stockholm area
4. Can you build this computer yourself, or do you need to buy prebuilt?
   I can build it but we are likely to buy a pair of them.
5. What are you current system specs?
   Not really relevant (but you may laugh to learn that I am running an Intel Pentium D CPU 3.2 Ghz with Windows XP.
6. What screen resolution will you be using?Doesn't really matter.
7. What websites/stores can you purchase parts from?
   https://www.inet.se (supposedly best)
   http://cdon.se/hemelektronik/datorkomponenter/ (often the cheapest)
   www.komplett.se
   www.dustin.se
8. Do you need to purchase peripherals?
   One computer got a screen and keyboard. The other need to upgrade at least the screen.
9. When do you plan to buy this computer/parts?
   Preferable 29th of December or first week in January.

[Adar]

Oh dear...

Now my mother plan to buy someone prebuilt from the store below. Does anyone have advice before she does so tomorrow?

http://www.alina.se/Produkt.aspx?T1I=252

The categories "Speldatorer", "GeForce GTX Gaming PC", "Hemdatorer" and "Företagsdatorer" contain the possible computers and all specifications are in English so you do not need to speak Swedish to help.

Are there any that do not seem crazy?

[Adar]

The store suggested this:

http://www.alina.se/Produkt.aspx?T2=POSEIDON-Q133

Is it a good choice?

[Adar]

And my friend suggested this custom solution which seem kind of neat.
https://www.alina.se/ShowCart.aspx?p...W-9060008-WW=1