This is how Expansion options work for Intel
Cpu to Gpu Expansion Options for full 16x support
http://ark.intel.com/products/75123/Intel-Core-i7-4770K-Processor-8M-Cache-up-to-3_90-GHz?q=4770k
Expansion Options 4770k
PCI Express Revision 3.0
PCI Express Configurations ‡ Up to 1x16, 2x8, 1x8/2x4
Max # of PCI Express Lanes 16 <----
So this only has 16 lanes for the gpu and if you run 2 cards they will only have x8 lanes from the cpu to the gpus
http://ark.intel.com/products/64595/Intel-Xeon-Processor-E5-2670-20M-Cache-2_60-GHz-8_00-GTs-Intel-QPI
Intel® Xeon® Processor E5-2670
Expansion Options
(20M Cache, 2.60 GHz, 8.00 GT/s Intel® QPI)
PCI Express Revision 3.0
Max # of PCI Express Lanes 40 <----
This has 40 lanes so you could run two 16x lanes from the cpu to the gpu and another gpu at 8x
Cpu to Gpu Expansion Options for full 16x support
http://ark.intel.com/products/75123/Intel-Core-i7-4770K-Processor-8M-Cache-up-to-3_90-GHz?q=4770k
Expansion Options 4770k
PCI Express Revision 3.0
PCI Express Configurations ‡ Up to 1x16, 2x8, 1x8/2x4
Max # of PCI Express Lanes 16 <----
So this only has 16 lanes for the gpu and if you run 2 cards they will only have x8 lanes from the cpu to the gpus
http://ark.intel.com/products/64595/Intel-Xeon-Processor-E5-2670-20M-Cache-2_60-GHz-8_00-GTs-Intel-QPI
Intel® Xeon® Processor E5-2670
Expansion Options
(20M Cache, 2.60 GHz, 8.00 GT/s Intel® QPI)
PCI Express Revision 3.0
Max # of PCI Express Lanes 40 <----
This has 40 lanes so you could run two 16x lanes from the cpu to the gpu and another gpu at 8x