I had a 100i and it was great until it got to about 2.5 years old. I was running a 4790k @ 4.5ghz and it would peak at 85c under load (BF4). However, I was using a custom fan curve as I found it better than the profiles provided by the software. 1k rpm isn't that quick to be honest so a custom curve would be worth looking at.
As for jumping temps, use CoreTemp as its more accurate, but also monitor your task manager, do you have any processes which are causing the temps/frequency to spike?
I ended up going back to an air cooler and so glad I did - so much better than the AIO I had - I was just lazy and didn't bother replacing it lol