I have two S3's, received last Friday. One of them hashes at 440GHs at stock speed (218.5), so I'm fine with it; however, the other hashes at 400 GHs at stock. I've been trying different things like putting it on a different psu's like ATX, Dell/HP server, but nothing helped. I'm taking notes on different clock speeds on this one:
Frequency GHS(avg) Temps HW Watt (Kill-A-Watt) ASIC Status
---------- ---------- ------- -------- ------------------ ----------------------
250 487.26 41, 41 2 428 Chain#2, 1 "x" on the far right
237.5 423.55 39, 37 38 367 All OK
225 422.69 39,36 7 364 Chain#2, 1 "x" at 2nd position & 1 "-" at 8th position from left
218.75 403.58 40, 38 0 355 All Ok
After editing the asic-freq file, a reboot command was issued. All readings were take at 30 minute mark. PSU is a Dell Server Power Supply 750W. All 4 PCI-E cables are plugged in, even at stock frequency.
Yes, it took me over 2 hours to finish writing this post.

I'm setting the frequency at 250, seems to be the sweet spot for this S3.
At what frequency would you run this at? Why?
If it works so well at 250, why the heck not? I would. Sometimes rebooting a miner from the webgui (NOT by powering it off, then ON) helps with "x".
I wasn't that systematic as most of my machines are best at stock freq and the one that could be overclocked is starting to produce 0.6%HW error on 237.5 and I dare not to OC it to 250mhz.