Running latest version of Photoshop CC 2017, I get major bad lag with zooming and with brushes when a layer that has been converted to a smart object is visible. If I turn off the layers, the brush is buttery smooth again. Efficiency indicator will drop during this lagg.
PC: 256GB SSD (photoshop installed here) - 6600k - 16gb RAM 3000 mhz - GTX 1070.