When I first considered this, I wrote to Pascal Oudet and he was very forthcoming with info...this is what he told me...
Hello Les
Pressure: as high as possible, without breaking everything ! I sandblast usually between 4 and 7 bars. But you need plenty of airflow, so a good compressor. The tank size doesn't matter, but the flow needs to be high (depends on your nozzle size, but 36m3/hour is a good basis, I'll let you convert in cfm if you're imperial).
But you're right, it's slow. i spend from one to several days on each piece.
Pascal
Hope this also helps...Les