I found a strange regularity. In hard tests like Catzilla 4k, 1440, 1080 and 3Dmark 11 Extreme I may set my gpu core clock on +60 from nominal. But in lower tests like Catzilla 576p, 720p and 3DMark 11 Basic I must make lower frequency, like +20-30 from nominal, or I have driver crash.
I don't like to use a UNgine Haven to benchmark, because I don't have a such resolution display. My display have only 1440x900 resolution.