I guess you're talking about water-cooling?
Haswell is pretty much the same for moderate overclocking like ivy bridge. Depending on the quality of your CPU you should aim for about 4,3 GHz for 24/7 usage.
Usually 1,25 Volt is enough on the vCore. Just keep track on your temperatures and don't exceed 80°C on the core. That should be safe.
For the detailed OC you should read a good OC-Guide tho. Can't explain everything in this one posting.
Sin made a good one for GIGABYTE but the process applies for ASUS aswell: http://forum.hwbot.org/showthread.php?t=78510