Q16 REG is the one you want it is the original formulation with MTBE in it. It is about 20ish HP better, combination dependent than new formula which is simply labeled Q16, we have tested it on the dyno and on track. It was introduced to get around some of the states that have outlawed MTBE. Then VP came back out with the old formula as they say by popular demand.
Also DO NOT buy it by the drum. Any exposure to oxygen will reduce its effectiveness. You are better off to use 5 gallon pails. We have even used nitrogen on top when we have an open can to keep the oxygen away. You could do the same I suppose with a drum but every time you use some the fuel will be exposed to oxygen and that will affect the fuel.