First of all I think I think is wonderful experiment!
Me personally I see 75% as a threshold for "supermajority" but not "consensus" and I think the two should be separated into two different categories.
I think with the 75% threshold the risk is still too high to have a large section of the community that disagrees with the decision of the MINERS lets not forget these are MINERs that are voting here, and so that section of the community could threaten to split the chain in the event of a fork.
In the interest of avoiding this scenario which could be argued to be the DEATH of Bitcoin as we know it, I propose that 90% should be the threshold for consensus. As we have seen with the XT proposal of 75% fork, we see a VERY LARGE and VERY DETERMINED group threatening to split bitcoin into two different chains. This should be evidence that 75% is not enough for a successful fork, and we should all push for 90% agreement as consensus!
In this video:
https://youtu.be/sE7998qfjgkAndreas Antonopoulos states that there is a voting period during which miners vote with their hashing power on the new version, and once a "supermajority" of 75% is reached this is a signal to the rest of the minors to agree to the new version, this is "the grace Period", once 95% of the previous thousand blocks are ALL signed with the new version, this is a "transition period", after 95% consensus is reached, then all none new version blocks are then considered invalid and are rejected as invalid.
So once the previous 1000 blocks reaches 75% it signals that the new version is required, and 95% signals that all non new version blocks are rejected.
Now I am confused as to what constitutes "consensus", is it 75% or 95%?
Also at the end of his video he shows that if you go against consensus and try to maintain an alternate block chain you will essentially be expending mining power for nothing and losing money. It makes more financial sense for the miners to mine the longer chain with consensus than it does to risk expending expensive energy to mine an alternate chain that is an extremely high likelihood of discontinuing and thus refunding all transactions and mining rewards that cannot be spent until after 100 blocks are mined anyway.
Miners would have to mine the alternate chain for 100 blocks on faith that it will be maintained for a full 100 blocks, risking waisting a lot of time and energy and money for nothing, when they could be just mining the valid chain that has reached full consensus for a change.
All transactions that are made on both chains during a maintained fork are known as "double spends" that are eventually refunded and erased from history.
Very informative video!