Download Trixx, you can change core clocks and voltages while they're hashing to get real time results. Once your change them in Trixx though, they all drop down in speed by like 10-15 hash and come right back up, so wait a second til' you gauge a reading.
They should be more stable at lower core clocks, that's why you start lower and work your way up, not the other way around
I'm running them from a headless linux, and afaik theres no trixx there, I can however easily adjust the clocks via cgminer, accessing the rig from my main computer, but thanks for the heads up on the 10-15 drop though.
I felt that I kinda started from the wrong way, but I had one card running in another computer, prior to buying 3 more, that I had been optimizing for 750KH/s earlier, and thats the .conf i started out with, in retrospect I shouldn't have because it caused a lot of trial/error with the cards that had higher stock voltage.