Looks like the SIG P227 is the winner.
"Any reason that DA/SA is a must? "
I definitely don't want to be the one to initiate a discussion about which is better, even inadvertently -- they're both good of course.
Partly this is user preference, the individual this weapon is for did formerly carry a Glock .40 and liked it OK, seems to like the SIG a lot more.
As for my criteria, while there's clearly no question that there are some great striker fired handguns in .45ACP and no doubt whatsoever that with adequate training the striker fired handguns are a good choice, just my opinion, in certain environments under certain conditions the DA/SA with the decocking lever offers some distinct advantages, both for safety and for staying in a ready-to-fire condition, which are two high priorities for me.
Big thanks to all who joined in here, this has been most helpful.