I tested my GTI2500 with the eagle eye coil last april and here is the results.
1st. test; A can 5" in dia. and 2 1/2" High with lid filled with mixed coins, rings, and dodad's.
Detected @ 32"
2nd. test; soda can standing upright.
Detected @ 27"
3rd. test; Stainless dog dish 11 1/2" dia.
4th. test; Cast iron skillet 2/3 full of lead
Detected @ 47"
5th. test; lead bar 20"x 4"x 2 3/4"
Detected @ 48"
6th. test; Water main's that run off the side of the street.
Detected with no problem but depth unknown.
This was a air test only except for the water main's.
As you can see it will go deep if you need to go deep.