Right Jessgo, and exactly Bill. I have a X-70 and GP-3000. Also the X-70(5) in relatively quiet goldfield soil (very low mineralisation) with the round 10.5" HF DD in Prospecting Mode will get closer to the SD/GP with the stock 11" DD for depth. But the X-70(5) diminishes much lower in higher mineralisation, with hotrocks, and when a bigger coil especially a Mono is put on a SD/GP.
The X-70(5) in Prospecting Mode(All Metal or zero-0 IM-Iron Mask) with the round 6" HF DD and 5x10" HF DD will pick up some specimen gold, sponge gold(small with holes in it), and micro grain sized gold that the SD/GP's will not even beep on. And the X-70(5)'s are better in trashy areas.
"X TERRA 70 VERSATILITY
This is easily the best goldfields detector(some would argue that the MXT, GMT, Lobo ST, or Infinium LS is the best) on the market under $2,500(this was written before the SD-2100 and 2200 prices were reduced to about $1,200 and $1,800 respectively and I think before the Whites TDI came out) when used with the optional DD coil. It is also the best beach/coin machine under $1200(some would argue the Sovereign, Quattro, or Safari is best for this). So it is a true all-purpose machine. The standard coil, while great on the dry beach sand and park soils, cannot handle the mineralized goldfields. Put a DD coil on it and it will handle the goldfields, even the noisy spots, provided you turn the sensitivity control down.
I did some depth tests in relatively quiet goldfield soil and was amazed at its depth ability--only down about 20% to 30% on the Gp3500! However this quickly shrank to about 60% less in mineralized, noisy soils. This is fine for the hobbyist but the serious gold hunter will need to fork out more for top of the range machine.
However, the Xterra 70 has some advantages over the top of the range GPs. It discriminates small junk targets out much better and it beeps on small gold specimens far better. By small specimens I mean fine veins and small rough pieces of gold in quartz rock as are commonly found on reef- gold mullock heaps or quartz paddocks. In fact some cagey professionals use the XTerra 70 especially for specimen hunting and for searching high-junk goldfield camp sites.
When in Prospecting mode, the character of this little hi tech machine changes. It becomes sensitive to tiny gold nuggets that it wont even look at in the treasure hunting-coin modes. Its discriminator will only reject iron at half depth, but thats enough to get rid of most junk targets. When detecting goldfield areas thick with junk, its best to sacrifice the tiny nuggets(and some depth) and select a coin(& treasure) mode where the discriminator will reject all iron and aluminum foil. At least it will pick up bits of gold as big as this letter O or bigger.
HANDLING
All the Xterra series may look light, small and unimpressive compared to their big Minelab brothers but thats what makes them a featherweight that any little lady or kid could swing for hours on end.
SUMMARY
If you can only afford one budget detector and want to prospect for gold as well as coins relics, jewelry etc, this would have to be the best choice for you. If you can afford a few grand for a gold detector then get a GPX 4000 or an earlier (SD)GP model and get the Xterra 70 for the little quartz-gold specimens and general treasure hunting."
