7970 will be faster
I'd buy the OCZ vertex 4
Depends on the manufacturer no card will overheat unless it's broken, if it did then the company would loose pretty much all it's customers and reputation
Buy the normal 7970 with a good cooling system and overclock it to 1Ghz
3.) Just by the not OC edition and then OC it yourself after you get it. If you dont know how, there are loads of helpful tutorials here and elsewhere. As for cooling, if you have a well ventilated case, it should be fine
For playing BF 3 on a 120Hz monitor(ASUS VG278H for nvidia,Samsung 950D for ATI), which one is better in performance/$?
#1. MSI N670 PE/OC $404.99
#2 Gigabyte Windforce OC $399.99
#3 XFX Double D FX797GTDFC Radeon HD 7970 GHz $439.99
#4 SAPPHIRE Vapor-X 100351VXSR Radeon HD 7970 GHz $469.99
I intend to buy 1 this month and then another one next month to SLI/CLX.
graphics cards are made from different companies like asus msi xfx and sapphire which one tends to be the best? i know its not performance but just like for cooling and quality, is sapphire the bestT? or msi ?
If I were you I go for the Samsung 830 series SSD, better performance overall than both the ones you listed, just read the charts here, better reliablity than Sandforce models like OCZ and better GB/$ than Intel.
There is only one significant difference between 3570K and 3770K: 3770K offer Hyper Threading which when turned on it will decrease your game performance anywhere between 5-25%, however it increases your CPU's performance in other stuff like Video encoding. If encoding video faster is worth $110 for you then go for the 3770K, else stick with the 3570K it overclocks just fine.
If you don't intend to extreme overclock( I define this as 4.6Ghz and above on a Ivy Bridge) you don't need any more water cooling than Corsair H60, you can probably go cheaper with a $30 air cooler like Hyper 212 Evo and do just fine in OCing in the 4.2-4.5Ghz range.
High end water coolers like H100 will be difficult to set up in a standard mid tower case, and cost your at least $20 more than high end air cooler like NH-D14,Silverarrow,Phantek PH-TC14PE which offers similar cooling performance.