Slow Network - Fedora 16 LXDE - Iptables or NFS

[Dors]

Hi guys, I just upgraded from Fedora 12.
Everything is forking fine, firewall, smb, nfs, the only problem is than my network is really slow...
I use nat to share internet and since the update is only slow on linux, If I use the connection from a windows pc everything works fine, but on the same pc using Fedora 16 it turns slow.
I used the same configuration on my Fedora 12 Server, transfering files with NFS was a bit fast 8MBps but on Fedora 16 it went down to 4Mb.
What could be the reason? Iptables or nfs configuration?
Thanks

BTW: Im using as client F16 64 bits and as server F16 32 bits