A typical US navy marine propulsion reactor puts out 250 MW. This railgun would require about 10% the energy output of such a reactor. A large aircraft carrier might have several cores.
From the 9/11 attack scenario below, impact speed matters (kinetic energy scales with the square of velocity), but chemical reactions pack a great deal of energy. The fuel of the airliners crashed into the World Trade Center towers released some 370x more energy than the impacts themselves, though as thermal energy delivered over roughly an hour, rather than the instantaneous impact.
As an alternative to missiles, the railguns would likely allow for increased firing -- a typical vessel carries fewer than 100 missiles, but could probably carry far more shells (and be capable of firing them).
I'm wondering at what point increased speed means you're simply punching holes through things without actually inflicting damage -- it's the transfer of energy from shell to structure that matters. If you're targeting a deeply buried concrete bunker, this is appropriate. Residential or commercial buildings, cars, etc., will to a large extent simply get very well ventilated (though you might not want to be in the immediate enting area when this happens). Matching shell structure to target likely matters.