I seemed to have had some success.

I have steped back the firmware to 055 and add the -speed=1 option to growisofs (so the disk now burns at 2.0x1385KBps).

Comparing the md5sums of both source and burned files is the same, so all is good so far.

Thanks for your help, I will probably provide an update in the non windows thread when I have had (hopefully) more successful attempts.