I want to report in on my findings, running a pair of S3.
One gets consistent 430GH over 1 day, 6 hours.  Default clock speed
The other one gets consistent 410 GH over 1 day, 6 hours.  Default clock speed

I've rebooted the slower one several times, and all chips show OK status.  They are on independent power supplies.  Only one miner per 700W power supply.

Only upside is temperature is consistently below 40.