[Richard L]

It is not easy to compare the two.

C16 raises the auto ignition point to resists knock at high boost. But expect higher combustion temperature overall. Forged piston and oil spray below piston is quite normal on these setup. Power limitation is cylinder temperature. I remember the Fi days in the 60's, producing 1000hp per litre, drivers has to run very rich to keep the engine from blowing up.

WI is reduces the high temperature spikes that causes irregular flame propagation speed, minimise the onset of knock threshold of pump fuel. Limitation is how much water one can inject before the spark plug fouls if the ignition system is not up to the job.

If both engine is tuned properly, water has a higher potential than C16. But you can go beyond C16, more exotic brews such as neat aromatic fuels. It goes on and on.