weird file transfer time problem

[vmos2]

I have three virtual servers, Server A B and C, all running the same version of debian lenny
A and B are on a vsphere virtual host, server C is on a windows machine running VMWare server 2
there is a folder on server A which is shared by NFS and mapped onto servers B and C in FSTAB.
File transfers to and from this drive take a couple of seconds between servers A and C, the same file will take a couple of minutes between server A and B
The same applies to transferring files by SCP, not just nfs

have the same entries in resolv.conf, servers B and C have the same spec, servers A and B are in the same VLAN, server C is in a seperate one
servers A and C have the same hostname.

I can see a few things that might cause issues between servers A and C but nothing that explains this, any ideas?