Cabinet : Nzxt Phantom Full tower ( Which color should i go Black / red / White )
Processor : I5 3570k
Gpu : Gtx 670 Amp zotac ( Has great custom support in my country + 5 year warranty )
Motherboard : Azrock Extreme 4 z77
Ram : Gskill 8 Gb ram x2 ( Should i go for 16 gb stick or 8 gb stick x2 )
PSU : Corsair Enthusiast Series TX750 ( U think it will be enough if i plan to go Sli in future )
SSD : OCZ Vertex 4 256GB ( I am new to ssd want it last good life if any other brand )
WD 2tb Black
WD 1tb green ( From my old system )
27inch Full hd samsung 1920x1080 ( don't want to go beyond Full hd as then game requirement get heavy on GPU )
Microsoft SIDEWINDER X4
Logitech G35 USB 2.0 Connector Surround Sound Headset
If your games are primarily from Steam, you have to install Steam to the HDD. Unless you employ some Command Prompt trickery, Steam requires all your game files to be inside its install folder and doesn't let you take it out of there. If you have a sizable games collection, that can quite quickly use up all your SSD space.
Image quality wont be compromised by having the large screen. Just some people think that at that physical size you should have a higher resolution, otherwise the pixels are "too big". But there shouldn't be any problems with quality.
A 3570k can get to around 4.2Ghz before needing additional voltage, so aim for that unless you want to get into the gritty side of overclocking. A 212 EVO will hold that frequency fairly well.
As for how much performance you will gain, it wont be that much really. The biggest difference will be in benchmarks.
Too hard to tell that far in the future, especially since the new console generation is happening fairly soon and that will (hopefully) raise the minimum standard for graphics.
Though I suspect it will be able to maintain 35FPS, but higher than that not sure.