Just got a Minelab 705 Gold with the 5x10 18.5khz DD coil. Dealer said it was the way to go as the 5x10 alone was a $200 coil. Great, but I'm wondering if a stock 9" 7.5khz concentric is better for coins. I mostly detect around sidewalks for coins. Pull tabs and foil are plentiful. From...