Clodmac, you could ring him to verify that the size is correct.
Another thing, you stated that he is doing all of this on his bench. Conditions are vastly different out in the field. However, if it is true what he is claiming, then it still gives you a good indication of how sensitive his mods are. I know my 7000 wouldn't pick up anything that small even if I rubbed it on the bottom of the coil in mid air.
You could also contact Mick at Detectronics Australia in Dunolly and ask him about his testing procedures as a comparison. I know Mick does mods on the 5000 to make it extremely sensitive to tiny gold. I don't know if he does the same sort of mods as Woody on the GP Extreme.
Good luck with it all. I know it is a big decision to upgrade an older detector for that amount of money. Makes my knees wobble.
Regards Axtyr.
G'day Axtyr my step son asked him directly on the Youtube thing if he had any 400th of a gram test nuggets for sale and the answer was he didn't have any , that was a few weeks ago and looking at his recent vids he is still using it . I also came across a vid from not that long ago where he had a test nugget that he claimed weighed 0.012 that faintly broke the threshold when touched on the coil . 0.0025 is roughly 1/4 of that and not possible with his modifications . I have spent a few hours looking at his vids from the past and formed the opinion he is ?
As for field testing he has a vid of his testing at a site with pipes horizontally drilled into the bank at various depths . Generally the target is placed in the pipe and the detector is swung over the top of the target , however his method was to place the coil on the ground and move the target backward and forward which would eliminate any ground noise ??
The stepson was looking into getting a modified machine , but with a limited budget the GP Extreme would of been his best option he thought after seeing the ballarat guys vids . the idea has been abandoned following a vid posted by the guy from Ballarat denigrating a Detectronics modified 5000 that he was given / borrowed to look at that had nothing wrong with it , following being called out by a number of viewers for unethical behaviour the Ballarat guy took the video down and admitted today in a follow up vid that he did not know how to operate or test it .
As you have pointed out the bench is vastly different to the field and on the Detectormods website the guy from ballarat pointed out that 80% of the goldfields are mineralised and normal timings as most of us know create noise , false signals etc and smooth timings like fine gold and enhance are far better options .
One of the very first things people do to upgrade the performance of a std machine is buy an after market coil , in my experience Mr Coiltek and Mr Nuggetfinder coils are an improvement on the factory coils provided by minelab , especially on machines specifically designed for mono coils . GPX 4000 onward . I don't know about the 7000 coils .
The guy from ballarat designs , developes and tests his mods using factory coils and older bundle type coils which he is of the opinion are better than flat wound .
I have spoken to Mick previously and again today , his actual testing is carried out in the field on known targets in mineralised ground on his property at Dunolly and any adjustments or issues requiring attention are undertaken in the work shop before retesting in the field before being passed
Mick has modified older machines in the past but highly recommends 5000 and 4500 as a far better option and superior outcome for the costs involved .
His costs to upgrade your 7000 would also make your knees wobble
Cheers Clod
or less. Both found with a PI and if you’re pinging this stuff with your PI I would say your machine is well dialled in for small bits. As small as I want to be finding anyway. 
