We own both the Coiltek 14x9 and the nugget finder Exceed 12x7 for our 6000s and they both work excellently, after havinf two coil failures with the 11" minelab units and as we are generally to far off grid we went with this set up.
The coiltek unit adds a bit of weight but can punch deeper than the std unit, it aslo picks up a lot of sub grammers i beleve more so than the std coil, the Exceed coil which we have only had the use of briefly appears to be equally as good both coils are quieter than the std coil in our opinion, we only had the Coiltek 14x9 for one trip last year and it produced 53 small nuggs for 14.7 grams over 5 days, at that time the Dragon got 21 bits with her SDC for just under 8 grams, on a recent short trip east of here to test her new 6000 with her Exceed coil and i might add it was frigging hot, we got 5 bits on a really flogged bit of pending ground which surprised me as we had chained that area a few years back and declared it devoid of the yellow stuff, so now its fishing etc till next Aprill then off tp the Mighty Pilbara for few Months and then we will see a far btter comparison.
As a footnote our travelling companion Pete has just done his 3 std coil and has bought a Coiltek 10x5 coil so be good to add thats performance as well.