Is this setup good for gaming?

I am about to buy a PC from Arbico.co.uk and this is a custom setup I have made:

Specs:

CASE: CIT Templar black
Main Board: ASUS M5A78L-M LX3 (Max 8gb ram)
CPU: FX-4100 (3.6Ghz 4 core)
Heat sink: Xigmatek Apache EP-CD903 (90 mm) - Will it be quite?
GPU: ATI HD 7850 2GB (Overclocked)
RAM: 4GB (Too low?)
PSU: 650W
OD: 22X Dvd

NO OPERATING SYSTEM
Cost = £506

I use my PC for mostly gaming/browsing/skype and occasional video encoding. I also like to have multiple applications open at once.

Would the games be slown down by the CPU?
How good is the GPU?
Is the website trusted?
RAM too low?
Is it worth it?