Every chip hits a point where the next increment of performance takes a large amount of voltage to accomplish. That is a good sign that you are approaching the overclock limit for that chip.
It will be interesting to see your result. It is a big drop down from 1.35 to 1.2875. I will be surprised if it works unless you were significantly over volted at 1.35.
My DO chip requires 1.36 vCore at 4200 and 1.44 to get to 4400 and that is with HT off (on for 4200). Every chip is different.