Dale has apparently been following some of the other traffic. He has his post up on scanning.
He has been hot on this for a while and has been working with Tenable on a series of plugins.
I am a bit more conservative but the white paper is pretty good.
I would work with the engineers to check against test systems first. Even in small shops there is usually one or more devices that they do their testing on before working on any others. In larger facilities sometimes it is a complete mock up (either virtural or real) of the entire system.
Then move on to the redundant/backup systems next. (often they are the same as the test systems perhaps that is why Dale didn't differentiate)
Two big items he didn't stress.
Document Document Document
Tell everyone exactly what you are doing and when.
Start with light scans
I use NMAP TCP connect with the fast scan to start
Add port 502, 2222 and 44818 into the list for the fast scan. (there are others dependant on your vendors)
If you are not specifically defining the timing chose the polite scan. (it really doesn't matter that much if you are only hitting a few systems)
It is almost never a good idea to scan entire subnets unless you have already successfully done dozens of other checks and know the network can handle it.
I think I will continue this when I have the time.