If primarily going after old silver then hit it first with Park 1 without changing the defaults at all! If the Park has lots of iron trash, consider LOWERING iron bias to better facilitate unmasking. The default performance settings are proven for 80 to 90 % of situations. If things are not jelling as far as deep recoveries, then consider lowering recovery speed or upping gain (but not both at once, initially) but be aware that you may also just be increasing the noise floor as well, so make only small adjustments to see if the improve or degrade performance. Per the manual, lowering recovery speed and swing speed can tend to increase ground feedback noise. Similarly, increasing gain may just increase the noise floor and/or falsing. There is no free lunch when it comes to maximizing detection depth, only meticulously balancing a number of trade offs to get the machine operating as quiet and stable as possible while maximizing sensitivity only to the extent you keep the machine on the edge of being stable/quiet.