Airport Extreme Speed Tests (2GHz vs 5GHz)

I tested a 702mb file transfer (sending and receiving) with the Apple Extreme 802.11n. One system (20" Intel iMac) is on ethernet and the other (17" MacBook Pro with 802.11n enabled) is using the wireless connection. I wanted to find out if I should be running 802.11n in the 2GHz or 5GHz range. I have always though the better the signal strength the better the connection would be, but my findings were completely opposite.

The laptop remained in a static spot with no microwave oven or any strange electronics around to interrupt. I transferred the file up to my iMac and back down and viewed the network traffic through the Activity Monitor. I also used iStumbler to check my signal strength.

I know my testing has its flaws, but this is what I came up with...any recommendations to get better speed or am I looking at the best case?
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Test 1:
2GHz - Channel 6
Signal Strength: 62%
File Send (Average/Max Burst): 2.6MB/s / 5.5MB/s
File Receive (Average/Max Burst): 5.8MB/s / 8.2MB/s
Notes: The speed is all over the place for both sending and receiving. The graph in Activity Monitor looks like a heart monitor.

Test 2:
5GHz - Auto Channel
Signal Strength: 35%
File Send (Average/Max Burst): 8.3MB/s / 8.5MB/s
File Receive (Average/Max Burst): 6MB/s / 6.9MB/s
Notes: The speed was not sporadic like the 2GHz test, although this time the sending was faster than the receiving.

Test 3:
5GHz - Auto Channel - Interference Robustness Enabled
Signal Strength: 36%
File Send (Average/Max Burst): 8.7MB/s / 8.8MB/s
File Receive (Average/Max Burst): 4.1MB/s / 5.8MB/s
Notes: Slower on the receiving than Test 2, but a bit quicker on the send.