my thoughts on the small vs large mono coil discussion - it really depends on the ground. If the ground is just generally high in iron content, and especially has some salt (even small amounts) then a larger coil will likely run more noisy, and a smaller coil will run better - the main reason being is that a small coil is less likely to saturate. If the ground is generally mild-medium, but has nasty hotrocks in abundance, then the reduced surface sensitivity of a larger Mono will do wonders, whereas a small mono will be picking every hotrock in the paddock.
Now this is all assuming the same timing, Rx Gain etc etc is being used, and the only variable is the size of the coil.
The smooth timings do wonders on ignoring high mineralisation, hot pockets of ground, and hotrocks, but what you will notice in particular with Fine-Gold and to a lesser extent Enhance, is that they still love buried charcoal, and they are more susceptible to EMI. So it can be a bit of toss up when you are in medium mineralised ground in a area with high levels of EMI - do you use Fine Gold, or Sens Extra with a reduced Gain? There's no right or wrong, but in my conditions, a ratty threshold due to EMI can be very counter productive, so I often opt for Sensitive Extra or even Normal, with a low Rx Gain, maybe even Quiet Audio, and then deal with ground noise using the old methods learnt swinging the GP series.
