Nitro, having used every model of Goldmaster as they came out, yes, the GMT IS the best of them all. The GMT will find slightly smaller flakes of gold then will the earlier Goldmasters, but more importantly, will help you keep in perfect ground balance, and will do so in the worst of soils.
Jangles, here in the Mojave Desert, in highly mineralized soil, the GMT will find flakes as small as 1/10th grain. If you don't want to find small nuggets, then, as you suggest, use a much less sensitive powerful detector, such as the Lobo Supertraq, or Eureka. But bear in mind that SMALL nuggets are what we professional nugget hunters call our "bread and butter" nuggets, those which constitute MOST of our income from nugget hunting. A while back a friend of mine and I ran a "competition hunt" on a well-worked nugget patch. When either of us encountered a signal, we'd call the other over to investigate, to see if his machine could also hear it. Of the 84 nuggets found with my GMT, his Lobo Supertraq could not sense even one, even when optimally-tuned, and using the same headphones as I. All of those 84 nuggets were too deep, or too small, for the Lobo to sense. Total weight of those nuggets was 121 grains. Yes, the Lobo DID get ONE nugget, which the GMT gave a much stronger signal over. It weighed 11 grains. Frankly, 121 grains is "mo' bettah" then 11 grains. Bad thing is that my pal has subsequently upgraded from his Lobo to a GMT, and now he does as well as I do.
John, the fastest method of tiny nugget recovery is the Jimmy Sierra Nugget Cup. In my latest book "Advanced Nuggetshooting - How to Prospect for Gold with a Metal Detector" I detail the use of the nugget cup. With the use of the nugget cup, often it takes only a few seconds to recover a target. Hope this helps; HH jim