'Just a reply to my own original post here for the future reference of others, or perhaps some additional advice from you pros...
I finally got around to buying and installing the PR511 motion sensor with dual floodlights. It looks like a solid unit and installation was a snap, but in the end it still doesn't allow me to do what I want to do....turn the floodlight OFF remotely. From what I can see, you can:
1. turn the PR511 "ON" using an X10 controller which keeps the lights "ON" permanently with or without motion (if you're having a party outside or wanting to work outside, etc.)
2. turn the PR511 "OFF" using an X10 controller; contrary to what you might think, this doesn't actually turn the unit "off," but rather puts it in normal "motion mode," ready to turn on when it detects motion. It does not turn the unit "off" like, say, a wall switch would
So this still leaves no way to actually turn the flood "OFF" remotely, say if you had really windy conditions and didn't want to be wasting energy and you didn't feel a security need was there justifying the protection. From what I can see, the critical link is still an X10 wall switch which I wasn't able to make work. At that point a "normal" (non-X10) flood would work just as well, although it wouldn't give you that capability to trigger other X10 modules if you were wanting that...
'Any additional thoughts/ideas appreciated
Coyotefred