The initial authentication process is carried out either using a pre-shared key (PSK), or following an EAP exchange through 802.1X (known as EAPOL, which requires the presence of an authentication server). This process ensures that the client station (STA) is authenticated with the access point (AP). After the PSK or 802.1X authentication, a shared secret key is generated, called the Pairwise Master Key (PMK). The PSK is derived from a password that is put through PBKDF2-SHA1 as the cryptographic hash function. In a pre-shared-key network, the PSK is actually the PMK. If an 802.1X EAP exchange was carried out, the PMK is derived from the EAP parameters provided by the authentication server.
This was extracted from here, which is teh IEEE 802.11. Look at the bold part.
To answer to your question, 1000 pmk/s is the same as 1000 k/s
I can suggest to you to use
hashcat for GPU or
genpmk/cowpatty to use rainbow tables.
aircrack only supports CPU.
Anyway, if you use GPU you should get much more ratio than using CPU if your graphic processor is powerful. The best way as always is to test. :)