Very very smallest the cracking speed 7870 XT

[epixoip]

This is likely your problem:

-w 2 --gpu-temp-retain 45

Get rid of --gpu-temp-retain and use -w 3.

Your 7870 is also clocked at 725 Mhz instead of 975 Mhz, so that's another problem.

For benchmark mode your command is incorrect. Your command should just be simply "oclHashcat64 -b -m 2500"

Where can I find a description of all key commands?

"oclHashcat64 --help" or read the wiki page http://hashcat.net/wiki/doku.php?id=oclhashcat