You are getting into territory with that 2500k where a LCS cooler isn't going to keep it cool at those speeds. Even decent beginner watercooling kits like the XSPC Rasa need to be something like the RS360 to handle the 2500k and 2600k above 4.25ghz...and especially 4.5ghz+. You will see load temps in the mid to upper 70's as you get to these speeds.
Between the Kuhler 920 and H100, the H100 is your better bet...but I'd strongly recommend fans in push/pull...and decent fans running 1800+ RPM and good CFM.
Once you get the 2500k and 2600k's above 4.25ghz...I really recommend a XSPC Rasa RX240 or RX360 kit...even the RS has trouble keeping up with the heat those dump at those speeds...an LCS cooler would really struggle.
You need some fantastic case airflow to use air cooling or an LCS cooler with that setup, or a good water loop...or minimum of a Rasa RX kit.