I think one of the best evidences we have is the level at which computers outperform the human mind in certain domains. An artificial general intelligence would have very low latency access to all these mathematical and computational tools we've invented (physical simulations, databases, theorem provers), and it would not need to mechanically enter program code on a keyboard, but it would be directly wired to the compiler. It could possibly learn to think in program code and execute it on the fly.

The computation environment of neurons is also extremely noisy (axons are not well insulated) and neurons only fire at 7-200Hz. Assuming noise and low firing rate do not fulfill a certain task in mammalian brains, this is another way in which silicon-based minds could potentially be vastly superior.

Thirdly, assuming sleep is not necessary for intelligence, artificial minds would never get exhausted. They could work 24 hours on a problem a day, which is possibly 5-10 time the amount of thinking time a human can do realistically.

And lastly, an AI could easily make copies of itself. Doing so it could branch a certain problem to many computers which run copies of it and eventually collect the best result, or just shorten the time it takes to get a result. It could also evolve at a much faster rate than humans, assuming it has a genetic description: possibly hours to seconds instead of 20 years. Anyhow, it could easily perform experiments with slightly changed version of itself.