does anybody know if adding extra cap pack may hurt or help esc keep cooler or anything else,want to do speed runs on 3s lipo,tc5 quicrun 120a esc,castle 5700kv motor.

My understanding of them is that they help supply a more consistent voltage from the battery .
I don't think it would help keep the ESC cool in any way .
If you have long battery wires or joins ( running parallel or series batteries ) they would probably help .