Slow xfers from 1 pc on a gigabit network

[alquix]

Hi
I have a gigabit network with 3 attached PCs, all dual core processors with 2 gigs of ram and sata hard drives (I like to stay current). 2 of them can transfer large Gig+ files at around 80MB/s between each other, but my box that I use the most only transfers at 40-50MB/s
All cables are Cat5e. All OS's are Win 7 x64. cables have been swapped and have not shown to be the problem. The NIC on the problem PC is the Dynex gigabit PCI adapter from Best Buy. NIC drivers have been updated to latest Dynex and realtek releases, with no success on either.
I can usually work through issues, but this one has me stumped :X

 

[VanillaGorilla]

Is there any background programs running when you are transferring the files? Are you transferring the files from PC to PC or from a local storage area to the PC?

 

[alquix]

no other processes are running. I guess I'm trying to feel for a response as to the Dynex NIC to see if it's known to run slowly