This is more of a general question, but... what is the advantage of having a "faster" client, i.e., one that executes contracts faster? Is it just that your machine will use less power and you'll have a lower electricity bill? Or have more resources left over for computing hashes? Or is there an advantage to be gained from executing the contract faster than your peers?

Can anyone recommend a mid-level description of Ethereum that is more detailed than Wikipedia but not as detailed as the yellow paper? In particular, I'd like to understand whether mining fees are paid for executing contracts or for solving hashes or for both; and how consensus works (i.e., how it is coordinated that, as Wikipedia says, "[e]very contract is run on every full Ethereum node simultaneously and the result is the consensus of the output").