Can't give you a definate answer but we ran a team mates shocker of my spare armie, with the armie set at about 450,.. we didn't see to many probs, it was consistant on velocity, all day.. and he didn't run out of air .. but it was a limited event..
Someone one told me that your output needs to be approx 2x that of the output on the secodary reg .. so I would try around 300psi, then if you experience drop off just turn it up untill the drop off stops