Hi Firey,
I've got a F1a4 with a 11" mono coil. I don't seem to get a lot of depth with it, but my unit hasn't been upgraded, other than changing the coil plug. It'll pick up a ring at about foot deep, but the small stuff i've only found shallow. It'll find bird shot easily enough, but not at any great distance, probably 3-4 cms.
Interested to see what depths you can get.
Thanks
James