ignafiltro :
I will further investigate about the performance increase, it would probably help a lot. Should be +20% for Crysis and a bit less for Metro.
About the cooling it should be OK if you have the radiator as an intake. I am assuming you have the EVGA GTX 980 TI SC version with the ACX cooler, if you have the blower version (I doubt) then the radiator would be better as an exit to prevent hot air into the GPU. If you want you can post a picture of your rig I can help you with fan placement.
I would just try doing it, if you just want to try how it works out without many tweaking try a 4.2 multiplier with no need to touch the voltage settings. If you like it then you can keep on overclocking (manually setting voltage).
I actually haven't built my rig yet. I'm just still debating what kind of parts I need, and what benefits they hold.
So, you were saying that I shouldn't go for this one
http://www.evga.com/Products/Product.aspx?pn=06G-P4-4992-KR
But rather this one?
http://www.evga.com/Products/Product.aspx?pn=06G-P4-4993-KR
In fact, I might not even go with EVGA. If there are other cards with the GTX 980 TI chip, I might look into them if they are in the same price range. (600-700 dollars) If there is a better performer, then I might go with that one.
This is what I'm planning to build:
CPU: Intel Core i5 4690K @ 3.5 GHz stock (I'm going to overclock to 4.7 GHz)
CPU Cooler: NZXT Kraken X31 or NZXT Kraken X41
Motherboard: MSI Z97S SLI Krait Edition LGA 1150
Memory: Kingston HyperX Fury White 1866 MHz Modules (2x4GB)
Storage: 1 tb WD Black AND Samsung 850 EVO 256 GB
Video/Graphics Card: (I'm deciding this right now)
Case: NZXT S340 White Steel ATX Case
Power Supply: EVGA SuperNova 850W (I plan to SLI and overclock, so I'm adding a little more wattage to allow for that)
Wireless Network Adapter: GIGABYTE GC-WB867D-I
What graphics card should I use?