I play on a 144hz monitor and cap Warframe at 120fps. In the Orbiter, it's relatively stable.
After doing an hour and a half run in Duviri, my framerate was dropping as low as 24 fps. That whole time, it was only using 4GB of RAM, and Task Manager was displaying 0% GPU usage throughout. CPU rarely if ever went above 25%.
I've tried switching to Classic graphics, but have seen no discernable change. I was not experiencing frame drops this significant prior to the uipdate.