Motherboard - good choice
got one of those in the post at the moment, really good for the price
CPU - intel i5 3570.. did you mean 3570k ? because that motherboard is quite good for overclocking, very easy. would really reccomend it, makes the most of your hardware.
RAM - 16gb is plenty! certainly futureproofing
PSU - dependant on what you plan on doing id say this is a good choice, this build could easily allow you to run dual monitors and as time goes on this is certainly a build that will be progressing i assume.. so if you can afford a psu that large now i would.
HDD - fair hard drive size, nothing really to go wrong, besides dodgy makes.. you can easily see them on amazon though with their poor ratings, just be careful where you buy it from.
Radeon HD 6870 - you certainly wont be bottlenecking!
id reccomend something atleast a little better, this EVGA GeForce GTX 650Ti is £99 this week..
http://www.overclockers.co.uk/showproduct.php?prodid=GX-202-EA&groupid=701&catid=1914
there is a new AMD Radeon HD 7790 out which is quite good for value
http://www.tomshardware.co.uk/radeon-hd-7790-bonaire-performance,review-32655.html
sounds like itll be a nice looking setup.. what case you going for?