Slow File Copy / Network Performance in OS X

[Outerlight]

Hi everyone,

I am re-posting this as a new issue from here as I discovered that it was not a hardware issue with my new MBA. Mods, please feel free to close/delete that thread.

My setup is a Windows Server 2008 R2 box, an Airport Extreme, and an HP unmanaged gigabit switch.

Here's what I'm seeing:
MBA OS X Gigabit Thunderbolt Wired: 40-50MB/s, stuttering while copying
MBA OS X 802.11ac Wireless: 10-13MB/s, stuttering while copying
MBA Win8 Gigabit Thunderbolt Wired: Gigabit maxed, constant copy
MBA Win8 802.11ac Wireless: 40-50MB/s, constant copy
Lenovo T400 Win7 Intel Gigabit Wired: Gigabit maxed, constant copy
Lenovo T400 Win7 Intel 5100 Wireless: 15-20MB/s, constant copy

Stuttering while copying refers to me seeing the network utilization in resource monitor on the server drop to 10% or less on the server side, and then spike back up to 40-50%. In Windows on wired on either machine, this stays at 97-99% while copying files from the same drives.

How can I resolve this substantial network performance issue with OS X?

Thanks in advance.