My Precision gate came with a .9 psi spring. I ran that for a bit, but without the boost controller being armed enough vac would build in the gate that the next cold start would have the wastegate open a little and be a loud exhaust leak. I ended up with a 3 psi spring and that's enough to keep the wastegate seated all the time.
Personally i'd run a spring even if it's the lightest you can find
Same here, just enough spring to keep gates closed. On a slightly different note I generally recommend running a very light spring on the BOV(s). They sound cool when you step off the gas with a stiff spring in them but if you pedal the car you may crack the throttle back open on a lot more boost than you expect. This is when a lot of cars are damaged and/or wrecked.
For a street vehicle with co2 on 100% of the time to keep it from hanging open at times off throttle (if thats what you do) seems like a waste of co2 when a 5 psi spring cut down some wouldnt be that much power gain anyway and should be plenty controllable