Dual GPU cards, PCIe lanes, and SLI configs

[Ninjanometry]

So, how do dual GPU cards (GTX 5/690s, Titan Zs, Radeon X2s) figure into this equation? If my CPU supports at least 32 lanes, and my board has at least two 16x slots, can I theoretically run two Titan Zs in quad SLI across 2 slots and have both cards running at 16x?
Question prompted by watching this video:

 

Edited May 20, 2016 by Ninjanometry
Changed post title to better reflect thread contents.

[GirlFromYonder]

7 minutes ago, Ninjanometry said:

So, how do dual GPU cards (GTX 5/690s, Titan Zs, Radeon X2s) figure into this equation? If my CPU supports at least 32 lanes, and my board has at least two 16x slots, can I theoretically run two Titan Zs in quad SLI across 2 slots and have both cards running at 16x?
Question prompted by watching this video:

 

YES, if the mobo supports it

[Rune]

Yes.

[Kapono]

16+16 is 32, so ...Yes!  

[Kirky2k15]

Not sure ive ever seen a mobo that supports 32 lanes, IIRC X99 does 28 and 40 depending on the CPU?

[xentropa]

3 hours ago, Kirky2k15 said:

Not sure ive ever seen a mobo that supports 32 lanes, IIRC X99 does 28 and 40 depending on the CPU?

Mobo doesnt have to have the exact number of lanes.  Just equal or more.  Two titans using 32 lanes on a cpu plus board that supports 40 will just leave 8 unused.

 

Op i love ur avatar

[NumLock21]

Only socket 775 has 16 or 32 lanes and that is provided by the chipset not the cpu. 

Now its from cpu so it's just 16, 28, or 40 lanes.

 

[Ninjanometry]

So it would seem that for quad SLI, two dual GPU cards might actually do it more efficiently or somehow, "better" than 4 separate cards, no?  That would be an interesting video for me.  
"4 way SLI showdown - 2x2 vs 4x1"
Hell, throw AMD in there too for 2x2 vs 4x1 Xfire with their dual GPU/x2 series cards
I guess an issue for that would be finding something apples to apples to do the comparison with.  I have one GTX 690 (dual GK104 GPUs on one card) and although GTX 680 is also GK104 based, it seems to have some slight differences.  In 2x2 vs 4x1 comparison I personally am not too interested in power consumption because OBVIOUSLY 4 cards will be very hungry for juice.  More interested in performance comparisons.
I guess it might also be interesting to see other dual vs single combos compared too.  1x2 vs 2x1, 1x2+1 vs 3x1...
http://www.gpureview.com/show_cards.php?card1=668&card2=667#

[Ninjanometry]

Here's an old 680 SLI vs 690 video, but I'm interested in seeing our guys at LTT (preferably Luke) do a more modern and in-depth comparison.  Those of us who have to build our machines from used parts are not running out to buy two 1080s or a Titan Z.  I just dropped around $300US on my GTX 690 last month, and while I'm not seriously considering another one (and with regard to the SLI lanes question I asked originally, note that my current mobo and CPU do not support 32+ lanes) I am always curious about these what-if scenarios.