AirPort Extreme (802.11n) File Transfer Speeds Over Ethernet

Question

I tested the transfer time for a 1.33GB file from one computer to another under four conditions. Both computers support gigabit Ethernet, and all cabling is Category 6.
Condition 1: Both computers were directly connected to a pre-gigabit AirPort Extreme Base Station (802.11.n)
The transfer time was 128 seconds.
Condition 2: Both computers were directly connected to an 8-port D-Link DGS-2208 gigabit switch, which in turn was connected to a pre-gigabit AirPort Extreme Base Station (802.11.n)
The transfer time was 72 seconds.
Condition 3: Both computers were directly connected to an 8-port D-Link DGS-2208 gigabit switch, which in turn was connected to a gigabit AirPort Extreme Base Station (802.11.n)
The transfer time was 55 seconds.
Condition 4: Both computers were directly connected to a gigabit AirPort Extreme Base Station (802.11.n)
The transfer time was 28 seconds.
Tentative Conclusions: Using a gigabit switch as the parallel connecting device when the router is pre- or non-gigabit is helpful. Using a gigabit switch as the connecting device when the router is also gigabit is hurtful with respect to transfer time.
I would appreciate any comments.

Answer 1

I re-ran the tests several times, taking care to "pre-warm" the connections by rebooting the router (and the switch when applicable) and making one false start, stopping the first transfer and then starting the timed transfer.
The transfer times when no switch was involved were virtually the same as I reported earlier, with the gigabit router significantly outperforming the pre-gigabit AEBS (it was 5.73 times slower). Interestingly, the transfers via the gigabit switch were virtually as fast as a pure transfer using only the gigabit router.
And there was no difference in the gigabit switch-employed transfer times regardless of whether a pre-gigabit or gigabit router was used. Here is my revised conclusion:
Using a gigabit switch with Apple's pre-gigabit 802.11n router overcomes the slowness associated with a pre-gigabit router provided that pre-warming techniques are employed.