You could give these 2 config files a try sometime:
https://github.com/ewanleith/Wordpress-Server-Configuration-...
https://github.com/ewanleith/Wordpress-Server-Configuration-...
Basically they make nginx cache itself, which combined with this Wordpress plugin:
http://wordpress.org/extend/plugins/nginx-champuru/
Makes things very minimal, no need for even a dedicated cache :)