Just finished for the season and I thought you might like some feedback. It turns out that the 7000 is far more sensitive to interference from the excavator than the 4500, and big coils more so than small ones. The 7000 was picking up an annoying level of interference 20-30 m away, even with the small coli. My partner also reckoned it was worse when I was idling than when working it. I use a 4500 and rarely detected when the machine was running but I could get to within 10 or so m without any problem. My advice would be to avoid trying to detect within cooee of a machine. You can detect - but it is more taxing on the brain than it need be and you will miss faint signals.
By the way, I used a new 17 x 13 nugget finder evo with my 4500 on the push and was very impressed. We did some comparisons with the 7000 and this is what we found:
The 4500 with the 17x13 coil had better depth than the 7000 with the 13 coil on a specie with about 10g in it (probably about 16-18 inches down). Tested all modes on the 7000 and sensitivity cranked to 20 and couldn't get a murmur out of it. The 4500 was in enhance mode and gain at 13 and it gave a soft but very clear inverted dig-me-up signal through a speaker when detecting slow and low.
On a bit bigger and slightly deeper bit, the 4500 gave a clear inverted signal but the 7000 with the 19 inch only just picked it up when sensitivity set around 13 or so. The signal only got 'reasonable' and comparable to the 4500 when the sensitivity was cranked to 20.
The 7000 was better on small ~0.5g bits at depth - quite amazing really.
The 7000 with the 19 inch coil and the 4500 gave comparable performance on 1/2 oz and larger bits. The 7000 was running sensitivity at 20 but not sure of the other settings.
Note This was in hard packed old wash in a creek bed under a couple of feet of silty loam that was sometimes removed and sometimes not. Also and importantly I have a fair bit of experience under my belt and a pretty good technique and you have to go low, slow and steady otherwise all bets are off. Different conditions might change the results but I wanted to be sure that the 7000 wasn't way better than the 4500 and that I wasn't wasting my time with the 4500. If so I would have to have bought a 7000 as we are trying to make a living out this. But after 5 months or so I am convinced that I wasn't leaving much (if any) behind that a 7000 could have picked up and I am happy to keep using the 4500 set up - particularly when looking for medium size bits and up. The 17x13 will pick up small bits (0.2) but it is difficult to pinpoint and they are not particularly sharp. When chasing small bits, and for general prospecting through spinifex etc I prefer to use the NF EVO 14 x 9.
Stingray