My best CTR was around 30% and its was not for just first 10-20 clicks. Avg CTR range between 8-10% which I believe can be achieved comfortably if you use targetted keywords, switch off content network & split test you ad copy
Again it's all relative to conversion: in other words if you're making money you may be happy with a CTR of 0.5% (maybe the price is high?); in other cases (lead generation) you certaily need a higher CTR.