Asus Z87 WS vs. Asus P9X79-E Ws Motherboard build

The LGA socket 2011 and X79 chipset support CPUs that give you 40 lanes of bandwidth The regular CPUs LGA 1155 and 1150 LGA socket with the Z77 and Z87 chipsets support 16 lanes of bandwidth. So that in a Z87 board you only have 16 lanes and one card will run at x16 and two cards will run at x8,x8.
On the LGA 2011 the 3930k and the X79 chipset have 40 lanes to slit up so that two video cards will have x16 each and three will have x16,x8,x8 and four will have x8,x8,x8,x8. In the bios of the Asus Rampage IV Extreme there is a page where you can see all 5 slots and what the bandwidth will be for each slot when a device is placed in a slot. This is a very cool feature that lets you place two video cards in the correct slots to get x16 each and also what will happen when a card is placed in one of the other slots , what effect it has on the bandwith for the two video cards.
There are two other pages that show a live feed as to what is placed in what slot and the same with the memory slots and which are occupied.
The OC tuner is an overlay on the screen for real time overclocking while in Windows.
I have to say this bios is the best I've seen and the features seem to be never ending, overclocking is the easiest also as it took no effort to have a 4.7 ghz clock.
I can't say what the WS boards can or can't do compared to the Rampage IV Extreme , but I have tried WS boards before and didn't think they matched up to the enthusiast boards don't forget they do design boards for specific use and if your in a work environment and gaming is secondary then you may want a WS board.
With a SSD as the OS drive the start up is less then 30 seconds and shut down is about 10 sec.

I'm currently waiting for the Asus Raidr PCI-E based SSD that will make use of system ram for a ramdisk and give preposterous read/write speeds.

I also forgot to address your last sentence in the original post where you asked about the Quattro card. There is a limit to how many video cards you can put in a computer without special chipsets and software. Four way SLI and Crossfire is that limit. So with two 690's that makes it four GPUs and four way SLI. Four way SLI is a bit harder to manage then three way or two way .