Advice for building a mini itx gaming rig for £300-£400

I'm wanting to build a mini itx gaming rig for under £300-£400 ($450-$600). I already have a GTX 660 Ti Superclocked, 8Gb of ddr3 RAM 1600mhz ram and a 2TB 7200rpm hard drive. Can some advise the best components for a mini itx build for the budget I have? I need a mini itx case to go with that as well. Also I maybe getting a intel 2500k 1155 CPU which will cut into my budget. Thanks in advance.

Sexiest mITX case comes in various colours- http://www.amazon.co.uk/BitFenix-Co-Ltd-BFC-PRO-300-KKXSK-RP-Mini-ITX/dp/B008BZVTX8/ref=sr_1_1?ie=UTF8&qid=1361879382&sr=8-1

Best price/performance ITX mobo-http://www.amazon.co.uk/Asus-P8Z77-I-Motherboard-Intelligent-Processors/dp/B007RHVDU0/ref=sr_1_2?s=computers&ie=UTF8&qid=1361879432&sr=1-2

You can go cheaper or higher on the mobo if you wish and 2500k's are still great so if you can get one for a good deal go for it.

 

http://cpuboss.com/cpus/Intel-Core-i5-2500K-vs-AMD-FX-6300

I saw on Newegg that i5 2500k costs 219$ while FX 6300 costs 80$ less, when we add your taxes from UK. It will be the same thing...

-edit- When I mean same thing, I mean the same gap betwen those two in the price.

i'd recomend the coolermaster 120 or the fractal desing node 304,because the fitfenix prodigy isint really small.