Yes it does support SLI.
It does 8X/8X, the top slot which is 16X with a single card diverts 8 of its lanes to the 2nd slot.
It is those two that you use.
The UD5H has a bit more expansion but nothing important.
http://www.gigabyte.com/products/comparison/list.aspx?ck=2&pids=4978,4979
-----------------------------
YOUR BASKET
1 x Gigabyte Z97X-UD3H-BK - Devil's Canyon Core i7 4790K CPU & Motherboard Bundle **£15 Saving + Gigabyte Free Upgrade + £30 Intel Cashback ** £397.98
1 x BenQ GW2765HT 27" Widescreen LED Gaming Flicker FREE Monitor - Black £319.99
2 x GALAX GeForce GTX 970 OC Silent "Infinity Black Edition" 4096MB GDDR5 PCI-Express Graphics Card **WorldWide Exclusive** £299.99 (£599.98)
1 x Avexir Golden Blitz 16GB (2x8GB) DDR3 PC3-19200C10 2400MHz Dual Channel Memory Kit (AVD3U24001008G-2BZ1SE) £139.99
1 x Corsair Obsidian 450D High Airflow Mid-Tower Case (CC-9011049-WW) £93.95
1 x EVGA SuperNova G2 750W '80 Plus Gold' Modular Power Supply £89.99
1 x SK Hynix 256GB SSD SH910A SATA 6Gb/s Solid State Drive (HFS256G32MNB-2201A) £84.98
1 x Cooler Master Nepton 240M AIO Cooling Solution £79.99
1 x Toshiba 2TB 7200RPM SATA 6GB/s 64MB Cache - OEM (DT01ACA200) HDD £59.99
Total : £1,884.54 (includes shipping : £14.75).
Some item prices have changed and some items are now better than others. That was £1915 a few posts up.
YOUR BASKET
1 x EPIC BUNDLE: Intel 4790K, Gigabyte Z97X-Gaming 7, Kingston 16GB 2400MHz Kit, Superflower 750W PSU & FREE STUFF!! **£50 SAVING** £570.97
1 x BenQ GW2765HT 27" Widescreen LED Gaming Flicker FREE Monitor - Black £319.99
1 x MSI GeForce GTX 970 Gaming Edition 4096MB GDDR5 PCI-Express Graphics Card £281.99
1 x NZXT H440 Mid Tower Case - Black £89.99
1 x SK Hynix 256GB SSD SH910A SATA 6Gb/s Solid State Drive (HFS256G32MNB-2201A) £84.98
1 x Cooler Master Nepton 240M AIO Cooling Solution £79.99
1 x Toshiba 2TB 7200RPM SATA 6GB/s 64MB Cache - OEM (DT01ACA200) HDD £59.99
Total : £1,512.02 (includes shipping : £20.10).

It does 8X/8X, the top slot which is 16X with a single card diverts 8 of its lanes to the 2nd slot.
It is those two that you use.
The UD5H has a bit more expansion but nothing important.
http://www.gigabyte.com/products/comparison/list.aspx?ck=2&pids=4978,4979
-----------------------------
YOUR BASKET
1 x Gigabyte Z97X-UD3H-BK - Devil's Canyon Core i7 4790K CPU & Motherboard Bundle **£15 Saving + Gigabyte Free Upgrade + £30 Intel Cashback ** £397.98
1 x BenQ GW2765HT 27" Widescreen LED Gaming Flicker FREE Monitor - Black £319.99
2 x GALAX GeForce GTX 970 OC Silent "Infinity Black Edition" 4096MB GDDR5 PCI-Express Graphics Card **WorldWide Exclusive** £299.99 (£599.98)
1 x Avexir Golden Blitz 16GB (2x8GB) DDR3 PC3-19200C10 2400MHz Dual Channel Memory Kit (AVD3U24001008G-2BZ1SE) £139.99
1 x Corsair Obsidian 450D High Airflow Mid-Tower Case (CC-9011049-WW) £93.95
1 x EVGA SuperNova G2 750W '80 Plus Gold' Modular Power Supply £89.99
1 x SK Hynix 256GB SSD SH910A SATA 6Gb/s Solid State Drive (HFS256G32MNB-2201A) £84.98
1 x Cooler Master Nepton 240M AIO Cooling Solution £79.99
1 x Toshiba 2TB 7200RPM SATA 6GB/s 64MB Cache - OEM (DT01ACA200) HDD £59.99
Total : £1,884.54 (includes shipping : £14.75).









Some item prices have changed and some items are now better than others. That was £1915 a few posts up.
YOUR BASKET
1 x EPIC BUNDLE: Intel 4790K, Gigabyte Z97X-Gaming 7, Kingston 16GB 2400MHz Kit, Superflower 750W PSU & FREE STUFF!! **£50 SAVING** £570.97
1 x BenQ GW2765HT 27" Widescreen LED Gaming Flicker FREE Monitor - Black £319.99
1 x MSI GeForce GTX 970 Gaming Edition 4096MB GDDR5 PCI-Express Graphics Card £281.99
1 x NZXT H440 Mid Tower Case - Black £89.99
1 x SK Hynix 256GB SSD SH910A SATA 6Gb/s Solid State Drive (HFS256G32MNB-2201A) £84.98
1 x Cooler Master Nepton 240M AIO Cooling Solution £79.99
1 x Toshiba 2TB 7200RPM SATA 6GB/s 64MB Cache - OEM (DT01ACA200) HDD £59.99
Total : £1,512.02 (includes shipping : £20.10).






