I run Fast OFF, Deep OFF and here's why:
1. Like some others have mentioned in here If you have Fast ON it will cut your signal short and give you LESS information IMO. When you're seeking extremely deep coins you want every bit of audio information you can get. Fast ON may be good in higher trash areas but for deep coins you shouldn't be hunting in high trash areas anyway.
2. I run Deep OFF because the Minelab manual even says that there is EXTRA FILTERING going on with Deep ON. Why would I want extra filtering when the purpose is to run as all metal mode as possible to get deep targets. Deep ON might help give a better target ID on the screen, but you should not be detecting by the screen numbers if you want deep coins. The pros who are digging 10" silver dimes are detecting by ear which is something you have to learn to do in order to find really deep coins.