Check this:
http://axefxtutorials.com/2015/12/ax8-cpu-usage-of-all-blocks-types-fw-1-00/
The Reverb block is disabled for consistency (you know what to expect), and because reverb is an effect that often can be missed.
Here's the FX8 chart
http://axefxtutorials.com/2016/01/fx8-cpu-usage-of-all-blocks-types-fw-3-00-public-beta-vs-2-00/