One thing which Noctua is really good about is if a new socket type is released then they will upgrade the mounts for their existing coolers and make them available free of charge for existing customers. Case in point would be the socket 2011 motherboards.
So investing in a Noctua cooler is not a dead end as opposed to many "cheaper" coolers out there.
Some other manufacturers also offer installation brackets for a new socket. You will have to pay but it still ends up being cheaper.
My point wasn't though that the Noctua would only benefit this particular system... it was that there would be more benefit in upgrading the socket
instead of upgrading the cooling.
Now i feel more confused.
Should i upgrade my motherboard / cpu ? I think, I7 920 is still a good cpu.
My experience was the opposite. When I upgraded my graphics from 560 Ti to 7950, I also had to upgrade my i7-920 to an Ivy Bridge because it just couldn't hold its own in CPU intensive games nor in CPU limited games. In both Battlefield 3 multiplayer (a heavily threaded CPU intensive game) and Alan Wake (a dual thread game), minimum framerates went from 40fps to 60fps as I upgraded to a 3770K.
Should i buy a cheaper cooler for overclock ? It would be much louder. For sure.
Not really, I think Noctua's quietness is overrated a bit. And you can always upgrade the fan on a cheaper heatsink.
The reason for OC is : my graphic card is GTX 660 Gigabyte Windforce OC. I want to upgrade it, and the next one it should be AMD R9 280X
And i think, if i leave the stock, my CPU, with AMD R9 280X it won't be a good idea.
At least, i've been adviced to do so.
So, the main reason for OC is the next graphic card - gaming
Unfortunately, no amount of overclocking of the i7-920 will guarantee that the 280X won't be limited by it. There will be situations where it's handling it fine, but there will be equally many situations where it won't. Think about it... you're trying to combine a mid-high end current generation card with a five year old mid-high end CPU.
Another angle to why you should upgrade: the longer you hold on to the i7-920, the more it loses its value. Sell it away while it's still a good CPU.