Motherboards with 3.0 x 16, Native /16/16/16?

Is it for gaming that you gonna assemble or are you involved animation (3D Studio max, Maya, Special effects, Rendering specialist, Auto-cad and may be any 3D related works ?

Can you have a look at this ? It has 3-Way CrossFireX, CrossFireX™ and NVIDIA® Quad SLI™, SLI™ etc..

http://www.asrock.com/mb/Intel/Fatal1ty%20Z77%20Professional/

Here is the list of Mother board list from NVIDIA that support 2/3/4 way SLI

http://www.geforce.com/hardware/technology/sli/motherboards 

Regards, Shiva

Here is some boards that specifically supports 4 way SLI

http://www.asus.com/us/Motherboards/MAXIMUS_VI_EXTREME/#overview

http://www.asus.com/us/ROG_ROG/RAMPAGE_IV_FORMULA/#overview

http://www.gigabyte.us/products/product-page.aspx?pid=4169#ov

Hope this helps you :)

Regards, Shiva

The number of native lanes is a feature of the processor/chipset with the additional lanes coming from PCIe Switches using multiplexing so even though the slots themselves are rated at pcie3 the effective rate can be limited by the upstream link to the processor and will be a function of motherboard architecture - this article helps to explain the detail:
http://www.anandtech.com/show/6170/four-multigpu-z77-boards-from-280350-plx-pex-8747-featuring-gigabyte-asrock-ecs-and-evga

These are examples of mobos with a high number of pcie3 slots with 16 lanes
http://www.anandtech.com/show/6228/asrock-x79-extreme11-review-pcie-30-x16x16x16x16-and-lsi-8way-sassata
http://www.asrock.com/mb/overview.asp?Model=Fatal1ty%20X79%20Professional