from what I've seen here in Alabama on very small pickers. By very small I mean it'll hit a piece as small as 1/8th. the size of a grain of dried rice.
Machines I tested in the area are the XTerra 70, Eureka Gold, Tejon, Lobo ST, and the F75 held it's own every way possible.
Actually found that the XTerra 70 worked better that the Eureka and so did the F75 ... all metal mode is KILLER on small items no matter if they are ferrous or not.
The Tejon just doesn't have as good disc and for that matter neither does the Eureka compared to the X70, F75 and I'd put the Lobo in 3rd. place for finding small gold.
Overall I feel like the F75 is a GOOD choice for prospecting, it could pick out a nugget surrounded by small steel buckshot with ease as did the XTerra 70 ... none of the others tested would do that.
Matter of fact, one of my hunting buddies has a Goldbug II that wouldn't hit these small nuggets any better than what we seen out of the XTerra 70 and F75 and he was really surprised.
Not much of a scientific test per-se but I hope this helps you some. I'm NOT a full blown prospector but I like to give it a go a few times a year.
Mike