@P-Funk: which stakeholders are the network? Because this set potentially changes every time there is a transaction. Polls and voting can only measure stakeholders at an instant-in-time, but both network stability and confidence in the economic value require a greater degree of stability and consensus over acceptable rules and rule changes. That is why, for example, soft forks typically require a large supermajority. There is no technical difference between a soft fork supported by 51% of the network and a 51% attack; the only difference is that an acceptable soft fork is widely supported by the larger community and a 51% attack is not. But technically, and in terms of on-chain voting, the two are identical.
It doesn't sound like xploited, creativecuriosity aka SuperClam, or dooglus will be making any changes based on a 51% simple majority of CLAMour proposal votes though.
The specific number is somewhat arbitrary. 51%, 52%, 60%, 75%? Is there really a number that makes a majority of stakeholders-at-one-time the "correct" behavior of the network as opposed to an "attack"? If there is such a number, who gets to decide what it is? I don't think it is possible to identify one without considering the wider community and longer term considerations, things which can't be measured by voting.