oclhashcat and apu a8 5500 different performances

[n_lona]

I have this problem launching oclhashcat64 -b i got

Code:

Hashtype: sha512crypt, SHA512(Unix)
Workload: 1024 loops, 8 accel
Speed.GPU.#1.:     1249 H/s

but if launch oclhashcat64 -m 1800 -a 3 admin.hash ?a?a?a?a?a?a?a?a?a?a? -i --incremental-min 7 --incremental-max 10 I got:

Code:

Hashtype: sha512crypt, SHA512(Unix)
Speed.GPU.#1.:     500-540 H/s

why?

Code:

DISPLAY=:0 fglrxinfo
libGL error: dlopen /usr/lib/i386-linux-gnu/dri/swrast_dri.so failed (/usr/lib/i386-linux-gnu/dri/swrast_dri.so: wrong ELF class: ELFCLASS32)
libGL error: failed to load driver: swrast
display: :0  screen: 0
OpenGL vendor string: ATI Technologies Inc.
OpenGL renderer string: AMD Radeon HD 7560D
OpenGL version string: 1.4 (2.1 (4.5.13399 Compatibility Profile Context 15.201.1151))