DFS share using FQDN very slow | OK when using UNC path?

Hi,

I have a 5 node File Server cluster with DFS setup - Windows Server 2003. (We have 15 Domain Controllers across 10 sites)
2x DFS referral servers
The shares from the DFS are being accessed by one main site.

User’s folders are mapped to \\company.com\Users\JoeBloggs
On Windows 7 these shares are very slow to open and opening Microsoft office files is unworkable, very slow freezing etc...

But,

If I open the share using the DFS UNC path \\company\Users\JoeBloggs - it works perfect, speeds are fine etc...

I have searched the web and tried loads of fixes. On the Client machines (Windows 7) Trust Centre settings, registry entries to disable file verification etc...

On the DFS servers,
Dfsutil /pktinfo looks ok
Double checked all permissions on DFS root right down to users directories - all looks ok.

Anyone see this behaviour before. It is only affecting the Windows 7 users, Windows XP is fine.

Thanks, Joe