1. There is a good amount of difference between M5A97 and M5A99FX. The former is based on AMD 970 chipset and a good budget board whereas the later is based on the most advanced AM3+ chipset, namely 990FX and targeted towards performance segment. It offers you more number of SATA and USB (both 3.0 and 2.0) ports, better build quality and both SLI and Crossfire support at PCI-E 2.0 X16-X16 speed. It also support Quad SLI or Quad CF.
2. HD 7870 LE and HD 7870 XT are same GPU and the names are given by different manufacturers, Sapphire and HIS. It is basically a stripped down HD 7950 and good amount of faster than the standard HD 7870.