aerys :
jimmysmitty :
That is pretty normal for idle. I have a 4670K at stock with a H100i and it idles around the same, maybe a bit lower as we are still in our colder weather season but normal for Intel is 30-35c (depending on your ambient) idle and 50-60c at stock settings (depending on your ambient and cooler). It might spike to 70c if you have it overclocked even more but that is fine as well.
Remember this; even a custom loop water cooling solution will at best keep a CPU at ambient while idle. The only way to get lower than idle is with peltier (cold plate/hot plate) or more extreme cooling measures.
can I still get lower Temp if i change the stock thermal paste of H100i and get artic silver 5 or better paste on it?
Nope. If what you said is true your CPU is idling at or near your ambient. There is no way unless you go to a much higher end cooling solution (think expensive and not easy to find like peltier which is like a fridge almost) which is not a good route.
Again, water cooling will not cool below ambient, in your case 34-36c.
As for AS5, it is not better than what Corsair put on there. They did a lot of testing and are using that because it seems to give the best performance with their system.