I just got my ProVari a few weeks ago. I love it.
As far as voltage goes, it pretty much depends on the resistivity of whatever you have stuck on there. Don't run low-resistance stuff at high voltage, it'll burn out really fast. Of course, since you're using a provari, not only can you probe the element with function Ao to find out the ohmage, but it'll actually refuse to provide power to a shorted element.
My advice is to pick up some 2.8-3.0 ohm stuff and let your regulated voltage provide the power. Every time you
vape, start low and clock it up until you find a point you like. Myself, I've got a torpedo
tank with a CE2 in at that clocks in about 2.9 ohm, running it at 4.6v. Works pretty well.
