I've been using Firefox 57.0, aka "Quantum", since the end of last week and have been loving it. It feels as fast as advertised and I haven't noticed any deterioration in rendering of pages.
I've tended to use Chrome as my work browser and Firefox as my personal browser over the past 4+ years. My personal browser just got a big upgrade. The Mozilla Servo and Rust Language teams must be feeling pretty pleased and they deserve it. Congratulations!