mcarterbrown.com is the site for you, endless discussion on it over there, I think the current conclusion is an old nelson built from a box of spares achived 60 (from the attic ep7 - search on youtube) and some people were reporting 50 from a regulated sniper.
Theres even discussions on there about the calculations of how much power there is in a 12 gram, and a thread with hundreds of pages called "project lepricorn" (or something like that) about designing the perfect valve.
the main things that us mere mortals can gain from it is that temperature is the biggest factor, followed by time between shots, followed by relative bore size (tight is better) followed by barrel lengh, followed by changer position (drop out valves do well). Beyond that you're into discussions about flow path, devolumisation vs tuning for liquid or gas only.
40 from your phantom is good, I change the co2 at about 20 or 30 depending on the temp on the day in my trraccer and on my VSC phantom I wait until I notice the pressure starting to drop on the gauge.
To give you an idea of how much the temp effects it I've seen 600 on the gauge on a fresh CO2 in the middle of winter and 1200 psi on a scorching day one summer.
