For starters, the 2 boards with the 970 chipset only have 1 electrical x16 PCIE, so none of them are good if you plan to go with 2 graphic cards. And they have differences in the Audio chip and number of USB ports, as well as one having connections for both PS/2 keyboard and mouse while the other only has room for one.
Check the comparison http://www.gigabyte.us/products/comparison/list.aspx?ck=2&pids=4717,4591
Regarding the 990, the 990FXA has 2 x16 PCIE slots while the 990XA has one x16 PCIE and one x8 PCIE, as well as having an extra chipset that gives it another 2 6Gb/s SATA ports... on the back.
Check the comparison: http://www.gigabyte.us/products/comparison/list.aspx?ck=2&pids=4672,3901
And here, the 4 cards compared: http://www.gigabyte.us/products/comparison/list.aspx?ck=2&pids=4717,4591,4672,3901
To summarize, get one of the 990 mobos if you want to go with 2 cards as having 2x16 or 1x16+1x8 will have little effect.
Please excuse my bad English.
Former gaming PC: i5-4670k@stock (for now), 16Gb RAM 1600 MHz and a GTX 1070
Current gaming PC: R5-7600, 32GB RAM 6000MT/s (CL30) and a RX 9060XT 16GB
Steam / Live / NNID : jonxiquet Add me if you want, but I'm a single player gamer.
