Learn to listen to the 6000 it tells you all! I only use the 17" coil and scrape with a mini digger generally 3-4" depending on conditions. I work an area which is a virtual ocean of metal scraps from the old boys (thanks a lot guys!) the depth of topsoil cover in these areas goes from surfacing calcrete to depths of 1M in topsoils, river gravels and saprolite.
Get under the metal skin and things change, I find many sub grammers and up to 40 grammers which are buried in highly cemented calcrete to 500mm with the 6k.
Have compared with a 7k and minimal difference but the 6k won the smaller ones, 7k made no difference with the big ones and did not find any others the 6k did not find.
All gold makes a different noise with the 6k depending on the ground its buried in and once you get used to its idosycrancies you can pick it 50% of the time. (yodelling in topsoil = nice sized deeper nugget or the finest bit of wire which you can hardly see (fly wire) or a nearby tin lid) (scrape all soil away to caprock and deep low to high signal = 2 grammers plus deeper in calcrete, dug until you get the coil overload beeps which means they are close as), (digging 2-300mm and still low/high you are onto a payrock
Never discount the "aw man junk again!" noise, I recently passed over a 7g and a 34g in a creek bed twice on first passes, as some will know creeks love to collect every bit of rubbish each rain that exists for many KM, these were sitting in a creek that in an area that has been slaughtered since the 1980s.
Some of the bigger nuggets have been in 500mm of the most hardest cemented caprock and taken hours to hammer out with a demolition jackhammer (go wide to protect the nugget) and very hard to pinpoint with the 17".
Pinpointers are a gimmick and useless and I have just got a Sadie for the 4500 to help with this, I would suppose a GM with the teeny coil would be even better, these nuggets generally start at 2 grams and upwards so should work.
My experience is the 6k will pick up nice deep stuff and I have also dig up noises that said "hello I am ground noise" for a 22g.
Moral is learn the noises dont whinge about them no matter now they sound.
Using the 6k is like handling an SS Commodore and the 7k like driving a Kenworth and in my usage the performance is similar but each to their own.
I have massive bursitis problems in my RH shoulder issues which just operating my excavator aggrevates and then the decector on top of than so in my situation the 6K is a winner ( the 7k was unusable for me after 15 mins, yes harness and swingstick for both plus Panadol Osteo/Forte etc, dont comment on the pills etc, I try avoid my meds and are none of your business its just a small example and yes I try alternatives for the flamers).
To sum up the 6k is a very capable machine that the 7k can mostly do in a lighter package and I highly recommend it, but get over its waffling and you will love it.