The beauty of the ProVari is that you can use any atty you want on it. It doesn't matter - you just adjust the voltage to accommodate it. What you're looking for is not a particular voltage, but the resultant wattage at the coil. Use an ohm's calculator to find out. Most people like between 8-10w. 9.2w is my personal sweet spot.
I've used anything from 1.5-3.0 atties on my ProVari with great success. It's an awesome device and you won't be disappointed.
Also, when u are constantly using 3.7 batteries above 5v do you reduce their lifespan as opposed to running them in the 4v range?
Nope. The ProVari has a capacitor that gives your atty the higher voltage. The battery has a constant output. That's also how you can still run the ProVari at 5v or whatnot, even when the battery has discharged down to 3.3v or less.
Also to answer your earlier question, yes higher voltage at higher resistances will give you better battery life (on paper, anyway). Personally, I don't worry too much about this though, as the regular 18490 batteries that come with it last me all day anyway.