gpu : watercooled ? OverClocked ?

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Hello
Hellô !

I'm catching informations about the gtx580's options.

Smicha, from this forum in this topic : http://render.otoy.com/forum/viewtopic.php?f=25&t=24408
compared the 580 with the 680 / The 580 used as reference was a watercooled and overclocked one.

I've seen more than a hundred dollars of price difference between models of the same serie (580)
between overclock and not, with 2 or 3 fans, watercooled or not, etc.
I'm really newbie in hardwares sorry (comin from mac !!)

is watercool necessary to get long render times without any heat alert (i mean press render and get back home stressless)
is it handy in order to work in a quiet unloud office ?
can we put 4 graphic cards watercooled in a workstation ?

Overclocking ... does it add really more performance ?
if so, what does this add, working with it ?

Also, some cards have 6+8 connectors some have 16 connectors,
does it change something on a motherboard that's 16 and 8 connectors onto it ? adding adapters for the 4 cards is it a good advice ?
does it change something on the power used, the needed power ?


I thank you very much,

Arnaud.