Hmmm strange, when i installed the 1709 on one of my PCs there was still the Option. So far i did not see the option only when i wanted to install a diff. language than the installed one - there was the option greyed out.
Regarding winflash ... you could try to flash from the dos prompt ->
1. open cmd as admin
2. atiflash -i
3. atiflash -f -p # backup.rom
That allows to flash even with an ID missmatch - but double check that the file is the right one - as if not you might have a new doorstop
