you asked about the firmware ...
i upgraded it to the latest version from TP-Link:
Firmware Version: 1.4.0 Build 110620 Rel.52053n
Hardware Version: TD-W8960N v3 0x00000002

the last 2 anonymous entries are mine ... forgot i'd need to login to the board.
(it's late)
someone from tp-link is currently on the case ... we'll see how good that is ...

update:
no input from tp-link, except for one of their uk support people advising to change the wireless channel to improve the connection speed ...

kindle problem solved by adding its MAC address to allowed connections on the router.

today i'm now getting
Line Rate - Upstream (Kbps): 984
Line Rate - Downstream (Kbps): 4951

and various speed tests now show:

4238 kbps (530kB/s) 829 kbps (104kB/s)
(http://www.mybroadbandspeed.co.uk/)

10/1/2011 10:49 AM GMT 31.185.144.33 4.22 Mb/s 0.83 Mb/s 37 ms Coventry ~ 50 mi
(http://www.speedtest.net/results.php)

01/10/11 11:47:17
Speed Down 4064.56 Kbps ( 4 Mbps )
Speed Up 817.36 Kbps ( 0.8 Mbps )
Port 8095
Server speedtest2.thinkbroadband.com
(http://www.thinkbroadband.com/speedtest)

which is the sort of improvement i'd hoped for originally.

huzzah!

hope it keeps chugging away for you