I'm not trying to tell you anything. I'm asking you to back up your assertions by citing the relevant code.
Do it.
Have fun. Where are you getting "95% and above is acceptable due to it causing the 'old chain' to die quickly"? Why 95%? WTF does "die quickly" mean?
Do you even code?
Quickly means everyone will jump ship as soon as they either realize that they're on the wrong fork or they see that almost everyone else has moved on. The difficulty will be way too high in comparison to the hashrate and will die. If you take the 75% to 25% option then you're essentially splitting the chain into two (not upgrading one). The exact numbers are debatable though.