Basically this is what happens when playing osrs (with any client) underthese settings
If you were to just look at the task manager, the cpu speed would pretty much stay under 2 GHz on battery and be fixed at 3.4 GHz while plugged in. As you would expect the fan never turns on while on battery and always turns on while plugged in when osrs ( is open.
However, there is no difference in in-game performance between battery and plugged in at all.
What i have tried is to incrementally lower the maximum processor state until my fans stop churning when i open osrs. From 100-88%, nothing changed whatsoever, but at 87% cpu usage was dramatically lowered. It is an imperfect workaround as thecpu is throttled to 1.5 GHz once you lower it below 88%. And there is a noticeable decrease in performance; fps is at the max of 50 with the first 2 figures, but averages 40 when throttled.
Ideally i want cpu power consumption when plugged in to be the same as when it is not plugged in. When i'm not plugged it, i get the same maximum performance but without any fans and peak cpu usage, but i have been unable to achieve that despite much tinkering with dell's power manager and the advanced power options.