$1000 budget Decent gaming pc

Hi there guys i am looking to build a pc to play witcher 2 on pretty high settings and future games like skyrim battlefield 3 etc.. it doesnt matter if i cant use amazing settings like ubersampling etc but i would like to atleast play games on a nice setting with smooth fps that is easy on the eyes. Currently i am usinga 9800gtx and an old duel core processor and i can only run new games on low sometimes medium i would like a significant upgrade.

I do not keep up with pcs like i used to so i am not sure what parts at compatible or good value for money etc so here is what i found so far.

GPU : http://www.netplus.com.au/product/VD5/VDGFGTX570/Graphi...

Was thinking this graphics card some of the other 570s are over 400$ and i just assumed it was based on brand and they are all pretty similar but maybe you guys can give me some insight if that card is decent.

CPU:

i5: http://www.netplus.com.au/product/ [.] ost-SB2500

This processor seems like good performance for money do you guys reccomend it?

Mainboard: I generally buy cheap mainboard but try to get atleast an ok brand because i just want the basics and to spend more money on GPU and CPU but you guys let me know if this mainboard is ok for my setup. Also what is the advantage of buying a more espensive mainboard?

http://www.netplus.com.au/product/MB2/MBINDH61BE/Mainbo...

Ram : http://www.netplus.com.au/product/MB2/MBINDH61BE/Mainbo...

Was considering this is 8gb nessicary these days and for the near future? i don't really know the difference between ram maybe i can find something cheaper.

Power supply: http://www.netplus.com.au/product/MB2/MBINDH61BE/Mainbo...

Will this power supply do the job? i would like to spend minimal on this component if possible.

Case: Ok now i have no idea what case to get.. i might just ask in the store but sometimes they try to rip you off.

Accesories:I have everything but i was considering a cooling device do you think i should for this setup? it sits under my desk and i play some pretty long gaming sessions.

Help would be amazing guys this is doing my head in seriously lol there is a possibility it will go over budget but that is ok.