It took longer, but 250/0750 also a dead end. Over 500 first hour, then down. After 3h down to 485 average, 458 last hour on the pool. All "o" on the chips and only 1 HW. Dropping to 243/0750 for the next run.
243/0750 also a dead end, dropped to 4h running average of 471, with last hour on the pool at 449. Trying 237/0750.
I also started playing with the slowest of the others (225 for 453, no voltage change). Trying 250/0750, and so far 2 hours in it is rock solid at the expected 504. Not going to count those chickens, will see what it looks like tomorrow.
237 was repeated "x" from chips over four reboots, so bailed. 231 was 428 over an hour at the pool, also bailed. That unit just doesn't want to OC. Reverted to 225/no-volt.
Other unit, however, continues to hum along at 504 after 5h. I do not understand these things.
I noticed that repeated x's clear when you restart cgminer e.g via the System Start Up tab (which also happens when you Save & Apply settings) - just saying so you can reduce your restart / reboot cycle length.
Been said a lot of times. S3's are the same, but different ..... most of the S3 variants in my stable run best at different settings, and those with the same settings, on the same pool, over the same connection produce differing results! So there goes.