I had a similar problem a while ago (although not to that extent). I assumed it was something to do with my VM connection. Speeds for individual files were always either much lower than they should be or fluctuated constantly.
A couple of months I installed Linux (previously WinXP) - everything else with my setup is the same. Speeds from VM servers are now a rock steady 2.4MB-2.5MB *every time*. I believe it is because Linux's TCP/IP stack is implemented much better.
EDIT - Whoopsy. I seem to have missed that there is a second page to this thread and that the problem is solved. Oh well, it may still be useful information to somebody!
Ed.