Some quick answers to your questions:

1) The EQ800 only works in the nails if set at 20KHz or 40KHz, single frequencies. Forget about "IQ" for these tests.

2) The Impact with a 7" CC coil passes all of the nail tests, in ALL directions.

3) NEW DATA: Given that the concentric coil seemed to be the secret sauce, I tried the MXT Pro with the 5.3" Eclipse CC coil. It also passed all the nail tests in all the directions, and in fact was the clearest good/no-good performer on coins. It could even pick up the small gold ring between nails, IF the discrimination for nails is set critically.

My conclusions from testing with nails is:

1) Use a small concentric coil.
2) Speed of recovery is the secret to picking out targets amongst heavily populated ferrous trash.