Overclocking the ASUS R9 280.

So is the above card with cooling DirectCUII TOP. It's not the temperature or the noise, everything is fine. The question is:
Looked at the reviews on their basis immediately drove chip from 980 to 1150 and the memory to 1300 (5200) 1450 (5800). The result: is stable and the framerate of the wild. The voltage is not raised. Went on. Acceleration to 1175 gave is not critical, but noticeable artifacts in the Witcher 2. Slowed down back to 1150, chip not touch. Empirically, caught up the memory to 1575 (6300), is the maximum possible value without removing the limit. Remove the limit did not become a more expensive. Artifacts there, but compared to the variation 1150/1450 variation 1150/1575 not only faster, but quite the contrary.
BF4 on ultra, resolution dimensions when 1150/1450 brought up at the training ground 90-95, critically did not fall, and sometimes accelerated almost to 100 and then 110. On 1150/1575 Charter to issue 80-87. I can't tell you exactly, down to the units, but nine of the dozen began to appear a lot less than eight. In Witcher 2 I can't say plummeted in the city, but in Bendyuha somehow plummets to 44 to 50 (later reduced to standard frequencies, but the fps continued to sink in the place, although I do not suffer). The most interesting thing in the forest near the bridge, where previously observed sagging (in fact, a small, one time on second down to 40, basically went down to 50) is now falling and is up to 30. 30, 36, 40 and so on. That is, in a particular forest area, the fps drops very specifically. And this is the account that basically gives 60-80 and 90-120. In short, what I'm getting at: how it to understand? Overclocking? After all, under moderate acceleration the fps was higher. Maybe raise the voltage? But by how much? A little on the Internet related 280, because I don't where to get information about the required voltage level.