Chances are that if there are any performance changes, it might even be a decrease in speed because of having to find .ackrc files. We haven't gone profiling 2.0 yet, but that's near the top of our list.
http://geoff.greer.fm/2011/12/27/the-silver-searcher-better-...
Anyways, I don't really have the time for long analysis posts these days. I'm busy working on something that captures value in addition to creating it. :)