What drives do you EXACTLY have?
The Beast kinda hit it spot on. Is your server doing anything while your trying to back up? Also what are the specs of the server?
96 hours is INSANE, that's terrible speed, somethings holding this back but we need as much info as we can get
What I would do in your shoes:
Junk windows 7 and put freenas on your box (low overhead and designed for this)
Get a cheap gigabyte nic on the freenas box (assuming the switch/router you have is gigabit and so is the ESXi Server your backing up from)
For specifics I'd have to see what kinda of drives you have, but setting up a ZFS array (raid 5) would be ideal.