Which Computer to Purchase?

I've been looking for weeks now at what new computer to get. I'm looking specifically for a platform made for gaming. I play DayZ and my current laptops can hardly run it on the lowest settings. I'm looking to be able to play DayZ with the highest settings possible and still have high FPS. I've done a lot of research and looked into a few laptops along with a few desktops.

Laptops: ASUS G750, MSI GE70, Alienware 14, MSI GE40

Desktops: I've looked at my local Craigslist adds and found what I thought was really good deals on desktops but I talked to my buddies father who owns a local business tech store and he laughed and said go ahead and buy used if you want junk. He wouldn't really explain exactly why I shouldn't buy the used custom desktops so I'm wondering if you guys could explain why I shouldn't go with it. Here are the specs for the two custom desktops:

Asking $700.00 Obo.
1 TB 5400 Western Digital Hard Drive
8 GB G. Skill Memory
CD/DVD Drive
AsRock Z77 4th gen Motherboard
Antec Nine Hundred-Two Light Up Case w/ Multiple Fans
Radeon 6950 2GB Graphics Card
Corsair 750 Watt Modular Power Supply
Operating System: Windows 7 Ultimate with key
Motherboard and Graphics Card Driver Discs

Asking $1,000.
It has the latest gen of the APU lineup, Richland A10 6800k Overclocked at aroung 4.7-5ghz to your desire. The 8670D on the APU is crossfired with an HD 7750 which is overclocked to 900mhz on the GPU and 1250mhz on the GDDR5 memory. The 8670 is overclocked to 1141mhz (I think, Ill have to check) Theres 8gb of ram overclocked to 2020mhz, its stock @ 1866. It has an SSD that makes windows boot in less than 10 seconds after bios screen. After the windows logo it just throws you in windows. It has a corsair H50(watercooler) in a push pull configuration It will come with your choice of windows 7-8-8.1.

I appreciate any help I can get with this!
 
Back