It is true you can go faster either by getting better fuel, or by adding more fuel. But there quickly comes a point where doubling your fuel doesn't double your speed. In fact the amount of extra speed you get by adding extra fuel is optimized at a ratio of 3.92 to 1. At that "magic number" the amount of energy in the fuel that gets transferred to the rocket is maximized (it turns out that 65% of the energy per kg of fuel winds up converted to rocket motion). At least 35% of the energy in your fuel will go into moving unburned fuel, not moving empty rocket.

And it doesn't matter what kind of fuel you use. The only way to get around this is to use multiple stages
in your rockets. I.e., the first stage will mass 3.92 fuel units for every single unit of first+second stage. The rocket mass, of course, includes a second stage, and THAT stage will also have an optimized 3.92 to 1 fuel to metal ratio.

A two stage rocket will go exactly twice as fast as a single stage rocket, because you don't have to boost all those empty tanks. The 3.92 number works out differently in a gravity field and in atmosphere,
but that's what it works out to in deep space, which is where I figure the Enterprise probes will be launched from.