i dont use panda, but i never get pres with HF and hit catcher.
If I'm not mistaken, MTS balances Hit Finder Refreshes with Hit Catcher Watcher refreshes. If you are refreshing HF once every second, and then add a 4 Watchers in Hit Catcher, then HF will slow down to avoid PREs. Then, you're avoiding PREs, but will miss HITs that reappear/disappear quickly.
Therefore, I rarely run more than 2 Watchers in HC while running HF.
The PREs only really start showing up for me, when I am running HF and HC and they start doing a bunch of other things in mTurk independently, like searches or browsing through batches.