Some of you are a little bit paranoid when it comes to overclock corruption or whatever. If I had things that required days or longer of non-stop run time, then I'd still overclock - I just wouldn't push as far as I normally do.
But otherwise, time is money and if you do right you'll definitely benefit from overclocking. My Titans are clocked 60% higher than the professional parts, and my 5960x over 45% higher than stock. Those gains are pretty linear.
Plus if your data if that critical, you should be making continuous backups outside of the main system anyway. 4Ghz is no problem for a 5820K and I wouldn't ever be worried about instability at that frequency.