Advice needed: File server for VPN - samba, NFS?

Hi all

I've recently set up a nice FreeBSD 7 box as a small company fileserver. Runs samba, OpenVPN, pf, encrypted drives and little else. It simply exposes a dir as a mapped drive for two windows XP clients - myself and my colleague.

When the clients are on the same physical LAN it works beautifully. BUT, over the OpenVPN link it's unusably slow. And I do mean unusable. I've tried the various samba TCP tunings, but have concluded from various sources that SMB is just not suited to a modest WAN connection, due in part to it's "extreme chattiness".

So I seek advice. Are there alternatives that are a) better suited for WAN use, and b) accessible to windows clients? I only know of NFS but have never used it. Any thoughts or suggestions?

/sim