Slow checkout page with FedEx enabled

Repeatable: Always

Steps to repeat:
1. Go to checkout with FedEx module enabled, Account information entered, Production Server
2. After entering zip code, "progress wheel" will spin for about 5 seconds.
3. After clicking on "My billing information is the same as my delivery information.", progress wheel will spin for about 5 seconds.
4. After changing shipping method (e.g from "FedEx Express Saver" to "FedEx Standard Overnight"), progress wheel will spin for about 5 seconds.

Expected Results:
Checkout page loads similarly as fast as D6 / Ubercart 2 / FedEx on a similar server configuration (~1 second of "progress wheel spinning")

Actual Results:
Checkout page takes roughly 4 times longer (~4-5 seconds of "progress wheel spinning")

Further Information:
When "Display debug information to administrators" is enabled, I noticed that 8 identical SOAP requests (with the exception of the time stamp) are sent when clicking on "My billing information is the same as my delivery information.". Four appear in the "Payment Method" frame, four appear in the "Billing Method" frame. I don't know if this is normal or expected, it seems redundant and perhaps might be the cause of the long "progress wheel spinning".

There's nothing particular special about my install; all other pages load fast.

I appreciate any help. I'm not a developer, but would be happy to help in any way that I can.