Karen --
I totally agree with Etrac Tom, on all he said. Lately I've been trying "deep on" with lower gain while working trashy areas; reason being is that it can make the shallow trash sound "louder" and the deeper targets to sound "softer" and perhaps with a little better ID -- kind of allows you to ignore shallow stuff (if you want to) and focus on the deeper (softer) hits. Otherwise, I usually use Bryce's settings.
Like Tom says, though, you gotta find what works for you; and then -- at least in terms of things that affect the SOUNDS you hear (variability, deep/fast response, etc.), you might want to LEAVE THOSE ALONE. Reason being, if changing a setting changes the pitch, or duration, of the tone, it can confuse your ears. Bryce has trained his ears to listen for VERY SPECIFIC sounds, and if you use fast=on, then like Tom mentioned it might "clip" your audio. Well, if you have spent months listening and training your ears as to what GOOD targets sound like, and then you switch fast=on, you might MISS a good target, as your ears did not quite "recognize" that "clipped" audio as being a good target. Make sense? Have you ever had a favorite song that you listen to all the time, and then you hear it live and it doesn't sound "right?" That's kind of an analogy -- still the same song, but the live version just "sounds" a little different, despite it being the same song. If your ears learned to prefer the "studio" version of the song, and they are used to how it sounds, your ears then may "not like" the live version, or vice versa. This principle is sort of why Bryce found the settings (in terms of pitch and such) that he likes, and then LEFT them there...so he is listening for those specific sounds that he has learned to RECOGNIZE, ones that usually mean "good target."
Hope this helps,
Steve