performance problem with Virtuozzo Server

[startup3k]

Hi,
i'm trying to install Nginx  to replace Apache on several Virtuzzo VPS. 
I'm experiencing a big performance problem.  On the same server and on
static files when acting as a reverse proxy, Apache is able to serve
something like 10mbps, Nginx stops at 100-200kbps.  This is the
configuration:

worker_processes  1;

events {
    worker_connections  1024;
}

server {
    listen       81;
    server_name  test.domain.com;

    location / {
	proxy_set_header  X-Real-IP  $remote_addr;
	proxy_set_header       Host www.domain.com;
	proxy_pass http://IP_ADDR_ORIGIN;
	proxy_store /var/www/cache/www.domain.com$uri;
	proxy_store_access user:rw group:rw all:r;
     }
}

No problem if it doesn't act as reverse proxy; at the same time Apache
with the same origin server doesn't have any problem.  Also Nginx
doens't have any problem in a similar server based on Xen virtualization
tecnology with exactly the same configuration.
May anyone help me?
Thanks for your support
Alex

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,180098,180098#msg-180098