Here's a draft of an experience report regarding Servo that was submitted to this year's ICFP: http://kmcallister.github.io/papers/2015-servo-experience-re...

Table 1 seems to give some relevant data:

      Site | Gecko | Servo 1 thread | Servo 4 threads
    -------------------------------------------------
    Reddit |   250 |            100 |              55
       CNN |   105 |             50 |              35

  Table 1. Performance of Servo against Mozilla's Gecko
  rendering engine on the layout portion of some common
  sites. Times are in milliseconds, where lower numbers
  are better.

Given the promising numbers here, I feel like the following bold quote from a Servo-related job opening at Mozilla is relevant:

"Our goal is nothing less than building the fastest and most secure browser engine, and we aim to succeed by miles, not inches. We aim for double the performance of current engines, with no crashes."

http://careers.mozilla.org/en-US/position/ollA0fw0