Need a board that will accommodate lots of add-in cards

[Rassilon]

I want to build an X79 system for my next project. I have 2 Radeon HD 7850's (with double slot coolers) I would like to use in CrossFireX mode. I also have a TV Tuner card, and will likely be getting a Zonar sound card (both are x1 pcie). I would also like the option of having another slot available for future use. My first choice would have been the Sabertooth since I no longer bother with overclocking and care more about long term stability. But the Sabertooth will only accommodate 2 other cards besides the 2 graphics cards. I really wish there were boards that were at least 14 inches long with lots of slots that would let me do all this and still have good airflow between cards. My other choice would have been a Rampage IV Formula but this doesn't seem to be available anymore. The Formula supposedly has good sound which would obviate the need for a Zonar, so it wouldn't need as many slots.

I have been looking at these boards:
ASUS P9X79 WS
ASUS Rampage IV Extreme

With both of these boards you put the graphics cards in slots 1& 4; leaving slots 2,3 & 6 available for other cards. The chart in the manual shows the speeds of slots 2, 4, and 6 drop to x8 when filled with graphics cards. But do the speeds drop if you mix in some x1 cards?
Can you do:
x16-x1-x1-x16-empty-x1
or will the 2nd graphics card drop to x8?

Are there any drawbacks to using a workstation board for regular consumer use?

[kkn]

It all depends on tbe sice of the graphic cards too.
3 slot cards may end up blocking pcie2 and 5 if your unlucky.

[martyn]

Has a Rampage IV Extreme with two Asus Matrix HD7970 Platinums in PCIE slots 1 and 4 - Sandwiched between these wide cards 2 1/2 slot each is a Creative Fatality soundcard, luckily its nice slim 1 slot. Slot 5 normally for a soundcard is covered by bottom Matrix and i think slot 6 also partially obstructed. If you do utilise slot 6 you will want a 1 slot card only in there due to board connections below for fans, USB Headers etc.

On this board with the GPU in 1 and 4 Crossfired you run at x16 and i am on Gen 3 - note, ULPS chenges setting between @x16 1.1/2.0 and 3.0

[Rassilon]

As I stated in my original post I already own the graphics cards and the TV tuner card, so I already know how they fit physically. That is why I did not list slot 5 as being available for other cards since it is covered by the second graphics card. My main concern was how the lanes are divided up among the slots when heavily populated.

Since my first post I discovered a review at:
http://us.hardware.info/reviews/2623/10/16-intel-x79-socket-2011-motherboards-round-up-asus-rampage-...

It says about the RIVE:
"The lane partition is a bit confusing, however. At most you can use four slots simultaneously. What's peculiar is that slot two and three are effectively one and the same slot. One of them has access to five lanes, depending on where you place the video card. The first slot always has 16 lanes, and slot four and five switch between a 16/0 and 8/8 partition."

To put it more simply I was wondering if these boards can simultaneously run 2 graphics cards at x16 with 3 other add-in cards at x1 speeds. The above quote would suggest not.