I have the NEL Snake, NEL Storm, and the Garrett 5x8. And the stock coil, of course. The 5x8 was the last coil bought and hasn't come off since I put it on.
I found an IHP at 9" in dry soil with it (verrry squeeky, but it was there). Went to a private permission in an extremely old part of Bagdad, FL this last weekend and didn't find any keepers. The ground is a carpet of iron. I may bolt on the Snake and try again, but that concentric will require me to slow way, way down.
The NEL Storm is almost a pound and half, swinging around a long way from you. I'm 6'4" and have the AT Max shaft extended as far as possible. Swinging the detector *plus* a pound and a half coil mounted that far away is a tedious chore. I've swung it twice since I've had it and my shoulder complained for days afterwards. I have no doubt that you get considerable depth when using it, but I primarily beep sports fields and newer parks, so I don't really need that depth. I imagine swinging that monster at the old Bagdad house would be pointless, with the iron blanket masking the deeper targets. Might be worth a try, though!
So another vote for the Garrett 5x8. This is a fine, all-purpose coil that is very comfortable to swing all day and has great depth.