It was 24 hour Orthos stable on air at 3.5ghz with a Scythe Ninja. I couldn't go higher until I got 1067MHz RAM, but at that point I already was using watercooling... 3.6ghz was with water + new RAM, I never tried air on it to check. The Rev 1 DS3 wasn't designed for the electrical load to stay stable though at 3.73ghz and I don't want to do mods to it, so I'm fairly sure the voltage dips are the only reason it's not fully stable beyond 3.6ghz. I am dieing to play with the much better P35 based DS3 boards which can handle the electrical load and absurd FSB levels.
This E6300 was bought at the start of August of last year and those early chips weren't as good OCers as the later editions, hence partly why mine has a high default Vcore at a mere 1.86ghz. Any non ES should be 3.5ghz capable at or below 1.475v if the rest of the system and air cooling is capable of supporting it.