Empirically, I found that a player achieved zero gravity in a trigger with a tick period of 10ms when the trigger applied 1.28 positive velocity per tick.
I don't actually know if triggers can achieve a tick time of 10ms though, so that might just be what happened on my computer or it might be a reliable measure of the actual limit of ~65 ms which would give you -20 units/sec^2, or whatever.
Just saying that you should always see what actually happens and not assume that your scripted thing is going to exactly match up with the engine thing.