Dear dave106 and all;
i tried your fantastic upgrade yesterday. This was my experience:
1- I works like charm!
2- you might find it easier to use Total commander to uncheck 'system' and 'read-only' in the properties of the windows folder on your charmer, before Unlocking CID (to avoid any error).
3- alternatively you might use Lockiwiz 2b from this forum to unlock and unlock CID first.
4- the ROM upgrade went fine, showed some error messages on the charmer screen (nothing to worry about) but did not indicate an end. I unplugged it after 20 minutes. It rebooted on itself et voila, it was up and running.
5- Changing the boot scrren went very smoothly.
6- I noted that the T-mobile customization (after the new config.txt) did not install at all. I had to manually install the CAB listed in the config.txt file to reload the MMS and GPRS settings.
But now my charmer has no T-mobile crap on it...
However, i did not notice any dramatic change in speed....