I don't think it would really matter much being as most seem to be iron, nickle, etc..
I assume most space rocks would read on the lower conductivity ranges.
Course, the better the machine, the deeper one would be likely to find them.
I've seen TV shows of guys that drag huge monster coils across the fields
with tractors. And he's found a few good ones. Naturally, if I was out looking for
those with my Ace 250, I'd use the 9x12 coil to cover as much ground as possible,
and get the most depth.
From what I hear, the desert can be one of the easier places to find those as you
can visually scan the area for possible targets which often will stick out against
the natural desert rocks. Then you can try the machine on them, and whip out a
magnet to get a further clue.
The guy with the tractor likes to do the big crop fields, say in Kansas, Nebraska,
etc..
Was just thinking.. Being those are pretty low conductivity ranges, it's possible
a gold machine might be a good pick. But like I say, if it's got metal, most
any decent machine should hit on it.