Need advice with a selling price for my system

Hi everyone,

I bought a Gaming PC around 2 months ago, but unfortunately i'm looking to sell it. I just have no clue what I should be putting it up for, given I've spent more money on it since I bought it.

If you guys could give me a rough idea what to expect, that would be great.

Here's my setup. I bought it for £775 when it had a GTX 550 ti. But I've upgraded the GPU.
I added some more fans, a fan controller, newer OS and bought a brand new headset.
I'd like to sell it all together for convenience, but if you don't think it'll sell like this, please let me know.

Condition : Immaculate
CPU : Intel i5 ivy bridge 3570k overclocked at @ 4.4Ghz (excellent temps)
OS : Windows 8 Pro 64 bit (I have windows 7 ultimate too, if prefered)
Motherboard : Asus P8Z77-V LX (Asus AI suite, GPU boost etc)
Memory : Corsair 8GB Vengeance 1600MHz
HDD : 1TB S-ATAIII 6.0Gb/s
Optical drive : 22x DVD+RW DL S-ATA
GPU : 2GB EVGA Superclocked Nvidia GTX 660 Ti + Intel 4000 HD iGPU. Can be paired using Virtu MVP (supported motherboard)
Sound card : Onboard 7.1 Audio
PSU : Xigmatek 500W Modular PSU
Cooling : 4 x 12" corsair high performance case fans.
Mouse/keyboard : Standard wireless Logitech keyboard and mouse.
Display : 23" LG E2342T-BN LCD Monitor
Case : Xigmatek Asgard
Extras : AeroCool touchscreen LCD V12xt Fan Controller (4 fans, 4 thermal sensors)
Headset : Turtle Beach Ear Force X12 gaming headset (Xbox360/PC compatatible)
Warranty : 3 years platinum warranty from purchase (2 years and 10 months remaining)

Thankyou