Oclhashcat running slow?

Hi
I have just purchased a Sapphire Hd 7770 and installed it in my system to replace my ageing card.

I am running this -

oclHashcat64.exe -m 2500 -a 3 -2 abcdefghjklmnpqrstuvwxyz Deepspace.hccap --session=Deepspace t?2?2?2?2?2?2?2
pause
pause

for a wpa attack, the "i" and "o" have been removed as they are not used apparently.

My question.... I am only getting 20,000 k/s when using this, however, on another programme that I have tested I am getting 40,000 k/s, I would like to use hashcat as my preferred proggy. Is there something I have missed in the syntax that will enable me to utilise the full power of my card and hashcat?

Rab.