The 90% is silly... how can consensus be two different percentages? It can't be both a vote and consensus at the same time. People either need to admit it's basically a vote, with different requirements for RfAs and RfBs, or change it so it's the same for both. You can't have both a voting % AND consensus.
It's "rough consensus", which basically means supermajority with a slight weighting of votes based on reasons given. It's not a pure vote (at least, it's not meant to be), but it's certainly not consensus. We rarely get a true consensus on any Rf(A|B) - it would essentially require 100% support (there is a difference between consensus and unanimity but with a format like RfA [which discourages discussion], that difference is minimal).
An interesting factoid: I work on three other wikis as well as English Wikipedia, and they all keep the same % for bureaucrats. I don't know why English Wikipedia is different. As I said, it's very silly, when all they do is the job of a calculator (and when they don't... guess what, it causes controversy!)
The requirements for crats should certainly be higher than for admins (since crats need to be admins too). That can be done either by people being harsher in their votes, by the required percentage being higher, or a combination of the two. Since people are a lot harsher in their votes, the percentage doesn't need to be much (if at all) higher - 90% is probably a little excessive.