In general, going to a lower pitch/higher diameter, you will see an increase in acceleration at the expense of top speed. Going to lower diameter/higher pitch, you will see an increase in top speed and decrease in acceleration. This is very much like the gearing in an automobile. With any given gear, you get a certain combination of speed and pulling power. The trick with props is to find the right compromise for your airframe and flying style. On that Kadet, you would probably be better served by the 11x6 than the 11x7 since you don't want/need lots of speed. You might want to also experiment with an 11x5 or 12x4. In the end, it all comes down to what you are looking for out of your plane.

Hope this helps.