With a custom water loop cooling I say you won't have trouble with 4.6 ghz, I have a friend who achieved 4.4 ghz with the Corsair H100 with a voltage of 1.275 (note that voltage you will need it). With the overclock he does not break over 51 degrees when stressed. You may want to post what your custom water cooling is made up of so when the water cooling experts read this they can determine if it is good enough. I assume any custom water cooling loop you spend over $200 is better than a H100.
Edit: Oh yes, Toms did an article/tutorial on overclocking a similar CPU the i7-3770k which is not too far from your CPU, maybe you should give it a read.
- Socialfox