I’ve done something similar. Except I’ve gone for a Nginx + apache setup.
Apache is set to port 81 (Simply so i can bypass Nginx easily), Nginx does a reverse proxy on port 80 to 81.
Primary gain to me is I get to continue to use Apache functionality (mod_php + the http svn module) with a config file I’m used to, and didn’t have to worry about configuring fastcgi PHP processes (a pain that’s always bitten me), and Nginx sitting passivly serving up the cached content.

In the process of setting that up, I dumped using WP Super cache, as Nginx is doing a far “better job”, I dont exactly have a high ammount of traffic, but my memory consumption is sitting nice, CPU usage is constant, and the logs indicate constant requests happening.