Something to note:
Overclocking the Titan is ridiculously simple due to the characteristics of GPU Boost 2.0 which raises the boost clock above stock settings if the Titan feels the temps are low enough to do so.
Reference clocks for the Titan are 837MHz base and 876MHz boost. By doing *nothing* more than increasing the manual fan speed to the max setting of 85%, the Titan will settle in at 993MHz. This puts the Titan's rating at 5337 GFLOPS FP32 for a standard edition card. Of course it might be a bit loud with the fan that high

If that bothers you, just pick up one of these
EVGA Titan Hydro Coppers 
This would allow you to settle the Titan in at 1137MHz without even trying very hard, and would also be quiet. It would also push the rating to over 6100 GFLOPS, over a 33% increase from stock.