Ok, here's the deal:
In fairness, if you have a poor cabling job, it could render the bottom PCI useless. It's possible. However, there are 2 considerations that could make a difference:
1) if you get the P182, you can cable it through the rear and then no blockages/interference will occur with the PSU cable coming up the middle, so that'll make a differnce;
2) depending on the exact layout of the PCI slots, there could be enough clearance to the bottom...since there's only 2 PCI slots to begin with.
So, depends on how well you plan on cabling the case, and whether you truly need SLI. Very few people actually need SLI....by the time you decide to "add a 2nd card", there are single cards out that will beat the dual, lesser ones that you'll have. I've seen it happen over and over and over. Unless you plan on going SLI within 6-12 months of a card's release, there's no point because the next card out will beat them both together. Also, unless you're gaming at VERY high resolutions, a single, faster card will more than do the trick. It will also generate less heat in your case, use less power, etc, etc. So SLI only makes sense in a very few select instances.
Where I'm going with this is that unless you absolutely need SLI (I doubt it), you're far better of getting a single PCI-e mobo that also has 3 PCI slots. Which.......also then lets you easily fit a sound card or whatever without any interference from the cabling if you don't wanna spend time doing a good cable job.
Ya follow?
So:
-gonna cable nicely, get the P182
-no cabling but no SLI mobo is ok
-no cabling but SLI mobo could have fit problems
My $0.02 worth is get a Gigabyte 965P-DS3, a P182, and you're ready to rock.