If you double-click the dial, the red numerical field should remain visible and become highlighted, and you can use it to manually enter the desired value.
As you noticed, the values are also displayed in the Advanced tab of the settings dialog. They should be editable there as well. I'm not sure why you were unable to edit them there, it could be a bug in the build you are using. If this bothers you, please try updating to the latest nightly build!
I also dislike the dials. You can't really rotate a dial with a mouse. I suggest a slider control with predetermined stops, e.g. perhaps 1, 2, 3, 4, 5, 10, 15, 20, 25, etc. Running a load test 41 times per second is not really helpful.
thanks for your input! The dials have the advantage of being unbounded, a slider has a min and max setting (for bounded values it would of course make sense). From a mouse-gesture point-of-view they both work the same, ie you click and move the mouse in a straight line up or down to increase the value. We'll give this some more thought..