Quote from TD80:
Someone with a sustained Sharpe of 4+ is either cheating (let's just file some of the HFTs into this category, OK?) or hasn't been trading that long. I've seen ~ a 3.5 for one of my systems over the course of a particular year but it is under 2 over 5+ years across all systems.
The $300MM LJM Fund (skew sellers) had a Sharpe well over 4 for going on a decade or more.