I have never setup an SLI or Crossfire system before so never really had a need to know this but now I have the option.
 
My question is kinda 2 fold here.
 
Firstly to set-up SLI or Crossfire on my board would i be correct in thinking to max performance i would have to use PCI-E slots 1 - 2 as the are both x16 slots although slot 2 is an x8 and x16 sli configuration.
 
if this is the case, due to the limited space between the 2 slots how does 1 maintain a sufficient airflow to allow decent cooling, as the top cards fan will be pushing hot air from that gpu on the underside of the bottom card causing either A) the top card overheating due to not being able to exhaust sufficient hot air allowing it to cool correctly or B) the bottom card overheats because the exhaust air from the top card is blowing directly onto the underside of the the bottom card heating the bottom gpu from the underside as well as it heating up from it's own use.
 
Now if the above in either respect is true then the next logical step to reduce excessive heat build up would be to use PCI-E slot 1 -3 however slot 1 is a x16 and slot 3 is only x8 which would imply if my thinking is correct the the top card would then have to step down to x8 to match the cards and this would then reduce performance ? please someone tell me this is wrong, if it's right then how would i reduce heat build up if i have to use slots 1-2 ? and how much of a performance hit would i take using the  slots 1-3 ?.
 
Also when running SLI or Xfire while using AIDA to monitor the system temps should i see both cards under a similar load or will 1 show more load than the other..
 
Sorry for all the questions but i am a multi gpu virgin so please be gentle and take it nice and slow so i can absorb all the juicy bits :)
 
Paul...

I would use PCIe slots 1 & 3 if possible.  That would allow for the best cooling.

Both cards when running a 3D app like a benchmark or game etc., you'll see both cards running at the same or close to the same clock speeds, load, and usage with SLI enabled.

paul1967 :  The X58 FTW3 has (2) 16 X PCIe slots (even when SLI is enabled and using 2 video cards) but the 3-way SLI motherboards only have (1) X 16 PCIe slot , and the other (2) PCIe slots are X8 when used in any SLI configuration.  The only time each PCIe slot may be X16 - is when they are used with only 1 video card.  So... it doesn't matter which PCIe slot you use on most motherboards with exceptions , 3-way SLI boards are configured that way.  It is not true 16X 3-way SLI.  It is possible with some motherboards that slot 1&2 are configured to communicate better , or have a little higher transfer rate than , say :  a configuration of slot 1 & 3 or 4.  But if that is not an issue with a 3-way SLI motherboard , then slot 1 & 3 is the best way to go , as per your query about the top video card drawing in heat from the video card working in slot 2.  If you must , or do , use a slot 1 & 2 configuration , where the top video card is drawing in air from it's bottom , it is possible with lots of different video cards to force air into their end with a fan centered on the top video card intake (unless of course there is no opening at the end).  If there is no opening at the end of the video card you can still cool the top video card with a fan forcing air down onto the GPU processor/s.  This will keep the top card cool , and you can also use RivaTuner or Afterburner etc. to set the top video card's fan speed.  This is the usual adjustment to make (adjust fan speed to 90%).  This works well because lots of video cards , have "built-in" step down circuitry , that allows the video card to drop the core speed and the memory speed , when not playing video games or running a very demanding program.  
 
Update :  In any SLI configuration the GPU in slot 1 (primary) will run at a much higher temperature than the GPU in slot 2 (secondary) [always].  Unless you set a profile for the GPU in slot 2 to run at overclocked speeds [then the temperature of GPU2 will rise].  SLI can only be appreciated when a very demanding load is put upon the memory via the processors.  It is totally up to you how you set the video cards up.  Personally , I like to play around with default values and tweek other things [this way I am not reinventing the wheel , just spinning it better].  Since any decent higher end video card now adays has a core clock of 900mhz & GDDR5 memory @3600+mhz effective , the temperatures of such cards will run in the 60*C range+.  This means that overclocking the core , is taking the card to 1000mhz+ , then you will see why GPU2 is like a reserve , when the temperatures are in the 70*C range.  Adequate fans are a must , and it is not uncommon to have a video card where the fan can run at 6000rpms , instead of the 3000rpm ceiling.  By looking at your specs , it's definately time to upgrade your PSU , as this could be where extra heat is coming from , and any inability for your GPU2 specs to come more in line with GPU1.  I like to use TechPowerUp's GPU-Z rendering test , which forces the GPU to run @ 100% , to see how many amps this will require.  I have tested lots of video cards but 1 in particular for example :  a BFG GTX280 OCE Edition [650 core clock default] , ran for 1 minute and drew 47 amps from the PSU.  While informations say that it runs at 24 amps [testing is not really running full time].  With SLI or Crossfire you need a PSU that supplies around 60-80 amps+ , preferably on a single 12V rail design.  When not using an adequate PSU that is peaking full time , it actually begins to run the show - which means any problems begin internally in the PSU and show up as glitches / problems or malfunctions due to ample overcurrent protection circuitry across multiple 12V rails.  

I forgot how great you guys were/are, like I said in my other post its been a while since I last posted as I had no need.
 
Thanks for the replies helping me sort this out guys..
 
To my shame it's not an SLI setup it's a crossfire setup x2 6950's HIS 2 gig cards.
 
ZROCKMAN your a hero br, I had my suspicions regarding my PSU, the chap my wife bought the cards from said that it was more likely to be the PSU providing insufficient Amperage across the 12v rail so thankyou for that..
 
NordicJedi - so im guessing that it's like multi threading on the cpu if the software doesn't support it natively it wont use it and so if a game I'm playing doesn't support the sli/xfire setup then again it wont use it and i should only see and increase in load and temps on the primary card.
 
So now i have explained to my wife that the supprise gift of the 2 cards is great an all but i can't use them because the PSU isn't up to the task her reply was "well we will have to see about that and has now started trawling ebay for new bigger psu to run the cards.
 
Now if there was some way i could convince her that all this wouldn't run on my current board and ram we could be looking at a whole new rig :)
 
I think after she gets the PSU i'll have to tell her that my case has insufficient airflow and that i need a bigger case then go from there lmao...
 
Again guys thankyou for you all your help...
 
Paul....
 
Update this is the 1 I was looking at http://www.super-flower.com.tw/products_detail.php?class=2&sn=17&ID=99&lang=  it may be a little overkill for my setup but at last it will last for most if any future upgrades...