First time ITX build and overclock

[ahgeez]

Looking to build my first Mini ITX gaming computer and having a go at overclocking too. I have put together a few mid tower systems but thats the extent of my experience.
Probably only going to aim for around 4.0GHz in terms of overclocking. Just want to do a quick check that everything will fit without any dramas(and relatively easy to install), and i'm not wasting money on stuff i dont need.

Intel Core i5-4670K 3.4GHz Quad-Core Processor
Antec KUHLER H2O 920 110.0 CFM Liquid CPU Cooler
Gigabyte GA-Z87N-WIFI Mini ITX LGA1150 Motherboard
Corsair Vengeance 8GB (2 x 4GB) DDR3-1600 Memory
Samsung 840 Series 120GB 2.5" Solid State Disk
Seagate Barracuda 2TB 3.5" 7200RPM Internal Hard Drive
BitFenix Prodigy (Black) Mini ITX Tower Case
SeaSonic S12II 520W 80 PLUS Bronze Certified ATX12V / EPS12V Power Supply
DVD Drive

I have an old DVD drive I will be using and will be getting a graphics card later on (have an old 4870 but pretty sure it wouldn't be worth putting that in confirm/deny?)
I think the main issue I have is the cooling. I read an article with someone using an H60 and they had to use a slim dvd drive and get an extra bracket to hold it, but I have read elsewhere that a single rad cooler is fine. I guess the other question is whether the watercooling is overkill if i'm only aiming for 4.0GHz? Was just looking for something different to install, but if there is a strong argument for going with air cooling I will change it.

[O-L-W-A-G]

Look at the closed loops with the thin rad and slim fans, those would easily get you to 4GHz and take a minimal amount of space. Just in general a good idea to get low profile stuff with a mini-ITX build, look at graphic cards with a two slot centrifuge, they are louder but they have a predictable airflow direction and are normally two slots instead of an open GPU cooler which are normally 2.5-3 slots.

EDIT: If you have the cash http://www.playtech.co.nz/afawcs0139235/CATID=875/ID=20635/SID=150535250/productdetails.html
It is a mix of coolers but it has one of the highest size:performance ratio