So Joseph, just to clarify a burning question you have posed this entire evening. No you dont Have to Have infinately adjustable voltage to get out of those tank atomizers you are so willing to part with.
If you decide to go with a Carto then it would behove You to try a lower ohm version like the 1.7ohm resurectors or 2 ohm boges and while you are at it pick up a 2.5 ohm and a 3ohm version as well, all single coil for your eGo. Now four plus boxes of cartos later you will have found yourself a better vape than the eGo c that currently sits atop your device BUT, now you will almost certainly have at least two thidrs of those cartos left over that are ho-hum and still have this what about the other thing that is going on over here....... happening.
If that seems like alot of work , well it would be. But you would know at this point if you even liked cartos enough to invest in a tank to feed them. Four boxes of cartos would be somwhere around twenty or thirty bucks, plus or minus shipping. Chances are you have to get them frome more than one place also so thats kind of a pain also. Looking at it a little differently may be the better remedy.
The Vivi Nova seems to be a complete solution for those of us who want to try something different without forking out a good chunk of our own time and effort to locate and purchase a whole bunch of gear we may or may not like. They include three coil heads that will allow the tank to be run as we see fit, for our given tastes and power on hand. The othe part of our wattage equation is resistance. Various resistances allows you to vape at different wattage output from the same voltage applied. The Vivi Nova allows the user at minimum the ability to change the coil simply and affordably while keeping the rest of the device in tact and useable for the next variant.
At any rate no matter which way you decide to go it will be your way, and it will almost certainly be better overall than the eGo c tanks that you are using now. Spending too much time deciding still will not answer any questions, pull the trigger on something. That will be the only way you are going to find what is your next step. Good Luck. Happy Vaping.