Reply to Traktor S4 vs TP2, Latency, and CPU usage?

Hey everyone,

I know this subject comes up a lot but I still have some questions. What is an acceptable latency for my S4? How much does latency change affect CPU usage? The only way I see how to change it is the slider in audio setup. See attached pic for my current settings on my first generation macbook air with Traktor S4 (I believe the default value was one increment less).
This leads me to my next question, I have both S4 and TP2 installed but TP2 seems to be quite a bit more CPU hungry and does't feel as stable as S4 (it heats up my computer faster and gets laggy). Is there anything I can do to change this or should I just stick with S4.

Thanks in advance for advice, its much appreciated!
Sam