Check out the thread in the detector accessories section. Recent testing has shown me this is probably the best all-round coil for the GPXs.
Settings can change a lot, but as a general guide, for medium soils I'll use Fine Gold, V. Slow Motion, Audio Normal, Stabilizer 11, Fixed, Gain 14.
For hotter ground, I might go Fine Gold, Slow Motion, Audio Quiet, Stabilizer 13, Gain 10
If the ground gets real bad, I'll go to Enhance and drop the gain a bit more.
Signal pretty much on 18 all the time. Tone set to suit your hearing. T Volume - I'm on about 12 with headphones.