Buying New Gaming PC, Need Thoughts?

Hi, as says in the title i'm planning on buying a new Gaming PC (which the seller built himself) and need a sort of review or your thoughts, The PC I curently have was supposed to work well with Gaming but it can hardly even play Minecraft Singleplayer without lag. The pc i'm planning to be is 400 Euros which and the seller has included a 21 Inch Dell 1680 x 1050 Monitor and a Keyboard & Mouse. And yes the seller is trusthworthy, Here's the specs:
FULLY INSTALLED WINDOWS 7 AND DRIVERS
CASE:
NZXT LEXA Blackline, Redline Edition Screwless design
MOTHERBOARD:
Asus Striker II Formula nForce 780i SLI,
POWER SUPPLY:
Thermaltake Toughpower 850W Modular
MEMORY:
OCZ Gold XTC 4GB DDR2 PC6400
CPU:
Intel Q6600 2.4 Ghz
CPU COOLER:
Akasa AK-965 Low noise
HARD DRIVE:
500GB Hard Drive 7200RPM
GRAPHICS CARD: Sapphire ATI Radeon 4850 X2 2GB
DVD-BURNER: Samsung burner SH-S203N
ADDITIONAL COMPONENTS
USB 3.0 Card 2 USB 3.0
Gigabit Ethernet
Graphics Card with support for 4 monitors
So what do you think? I want to be able to play titles like Skyrim on Ultra with mods, Watch Dogs, Borderlands, Maybe Elder Scrolls Online and GTA V when it comes to pc and more, Will this be possible with these specs? Can the games run smoothly on hd? He said the processor can be pushed further. He also said the graphics card might be old but it's really powerful, Thank you