No benchmarks but my initial impressions have been: nightmare.
Word of warning if you're installing on Win7 64, I had a hell of a time just getting it installed and I'm not the only one:
http://forums.adobe.com/thread/628980 - there are some fixes and workarounds in there if you get similar problems. Seems to be all to do with permissions, I had to do a lot of registry hacking.
I then couldn't get any Quicktimes using ProRes codecs into AE without the Adobe QT32 server crashing (causing said quicktimes to stop working). These clips were still working in AE CS3 with no problems. This was eventually fixed by giving the QT32 server firewall access (apparently it communicates through TCP) and updating to latest version of Quicktime (I was on 7.6, newest version is 7.6.6).
Still haven't had the chance to put it through it's paces but wondering what other issues are round the corner. The joys of the early adopter... :/