I have been using an F5 for about 4 months and have found over 200 coins. I found a nice F4 on ebay with the 11" DD coil and an 8" coil. I took it out tonight using the 11" DD coil to one of the same places where I hunted with the F5 and in 45 minutes found 5 quarters, 10 copper pennies, 1 dime and 2 zinc pennies. The dime was the deepest at 6" and a solid 70 id. Do you think the DD coil makes that much difference? If so I can't wait to get the 11" DD coil for the F5.