The 8” and 5.75” concentrics are probably all you’ll ever need on any 5 pin, land Tesoro. They’re the two I like the best everywhere I usually go hunting. My Outlaw and/or Bandido always wears one of those, and I usually have the other along as well, on a spare detector. 8” for general use and good coverage, 5.75” for trashier spots.
The Mojave comes with the 7” concentric which is another great coil, but it’s right in between the 8 and 5.75. Since you have 8” already, save your money and get only the 5.75.
I suggest using the concentrics for best discrimination. I only use a DD/widescan where I expect -highly- mineralized soil, or just plan on digging everything. Only real advantage a DD has over a concentric (on a Tesoro) is beter ground coverage. Discrimination always works better with the concentric, depth will be close the the same with either.
BTW - I found the CORS Fortune I had to be no deeper than Tesoro’s coils and no more sensitive, but slightly heavier to swing for its size. Nothing magic or special with the NEL/CORS, but I never tried the bigger ones.