Gday
I found back when I had an extreme that the best all round coils for it was the Coiltek 14" round dd pro coil, minelab supergoldsearch 11" dd, coiltek 11" mono, and the minelab 8" supergoldsearch mono, using the dd coils in the hotter ground and the mono's when the ground conditions allowed.
The later flat wound coils are better used on the gpx machines, nuggetfinder evolution and coiltek elite etc, they say that they run on the Sd and Gp detectors and they will of course but they also state when ground conditions allow, so in some areas you may find them very difficult to use, I found the above coils worked best for me here in WA but also the later version coils were not available then either.
Best way to find out is to buy or borrow some coils and do your own testing in the field.
cheers
stayyerAU