Archangelboy :  I wouldn't consider a PCIe SSD for your machine , due mostly to the fact that you would need to also use a i7 980X or 990 CPU , to match the speed of the setup.  With a PCIe SSD the speed of them is really high , but they are best used with an overclocked to the hilt system throughout , that isn't in a SLI configuration for graphics.  Using a very expensive video card that costs $2000 - $5000 by itself on 1 of the PCIe slots.
 
At the price and storage size , it would be best to get (2) SSD's and not have the PCIe HD subjected to any heat from possible GPU's installed on the PCIe slots.  Even a SSD can be overheated by other system components , and cause them to fail or malfunction prematurely.  If you did install one , it would bump the rest of your system requirements to maximum to see the benefits in speed.
 
Sure you could do this if the PCIe SSD has a specification that falls under the PCIe 2.0 specification or less.

Archangelboy :  OCZ has just released (Jan.05/11) , 2 new types of SSD's.  The Z-Drive R3 (PCIe SSD)/Sandforce Controller/OCZ's first PCIe Sandforce SSD/Tier-0/1 data applications/1gb read - 950 write speeds/up to 1.2TB capacity.
 
OCZ has also just released it's new Vertex3 Pro SSD/Sandforce SF-2000 controller/Sata 6gb/s | read/write = 550mb/s [for SATA III connections.
 
This breaks new ground for me , as when I do go SLI (waiting for GPU's this week) , where I will install them into the #1 & #3 PCIe slots (enables both @ X16 speed on EVGA X58FTW3 mobo) , I can also still install one of these Z-Drive R3's in between the (2) video cards and it will still allow the center located fan on the #1 slot GPU to draw air without a tight obstruction , other than the Z-Drive itself.  Price will be the factor vs. capacity , but I could also use the new Vertex3 SSD's as well.
 
The Z-Drive should be compatible on any PCIe slot , as long as the PCIe slot conforms to the new 2.0 specification (which the Z-Drive will).  This means you can boot from PCIe - on any mobo , especially with the Marvell Raid controller capability.

Archangelboy
Will these boards support boot over pcie?

 
Absolutely, I do it every day.  You will have best results by using the latest BIOS (77 or later) for the X58 board. 
PCIEx SSDs are ideal for your OS and the primary apps that you would normally have on your boot drive long term, but stay away from the original Revodrive (non-X2) versions due to the firmware, the RevodriveX2's are more mature in that sense. 
I have used both versions, there is no comparison.  
 

ZROCKMAN
I wouldn't consider a PCIe SSD for your machine , due mostly to the fact that you would need to also use a i7 980X or 990 CPU , to match the speed of the setup. 

Inaccurate, Revodrives are PCIEx4 drives, it won't cause him some kind of bottleneck....920 or not.

ZROCKMAN 
At the price and storage size, it would be best to get (2) SSD's and not have the PCIe HD subjected to any heat from possible GPU's installed on the PCIe slots.  Even a SSD can be overheated by other system components , and cause them to fail or malfunction prematurely.  If you did install one , it would bump the rest of your system requirements to maximum to see the benefits in speed.

Heat is not an issue unless you have absolutely inadequate air flow, in which case it wouldn't matter what type SSD you had. 
 
Take a look at the photo of my system in my mods rigs page, you will see there is plenty of room between the RevoDriveX2 and my vid card, it will also fit between vid cards just fine.     
    
EDIT: Sorry, forgot to mention, although PCIEx drives might fit inbetween vid cards ok, it is recommended they be installed in the PCIEx slot farthest from the CPU....not saying it will or won't work, it is just what is recommended (by OCZ at least)

If I'm not mistaken the read/write times are double or more the standard SSD.. so in theory you should expect anything that has to open up to do so within 1-2 seconds instead of 5-10.. SSD's are easily the best upgrades to make you feel like you have a new system!