I'm on a macbook air and i can't seem to get more than 700 khash/sec

any suggestions?
 ./DiabloMiner-OSX.sh ... -w 64
[6/4/11 12:24:51 PM] Started
[6/4/11 12:24:51 PM] Connecting to: http://..../
[6/4/11 12:24:51 PM] Using Apple OpenCL 1.0 (Dec 23 2010 17:30:26)
[6/4/11 12:24:51 PM] Added GeForce 320M (#1) (6 CU, local work size of 64)
442/619 khash/sec