I have had the 13x17" coil for my CTX for a year now. I did not use it a lot last year. Maybe close to 20 hours. I also have a 13" Ultimate for my Etrac which I have had for 3 years. I have a couple of 'secret' places that I had a good amount of deep finds with the Ultimate coil. I can honestly say I have not found any more coins in those couple of places with the 13x17" coil. I am sure the 13x17" coil is OK because I do find deep coins with it in other places. It just doesn't beat the 13" Ultimate. I run auto +3 and it registers 27-28, Ferrous Coin and Combined with an open screen. So my ground is fairly mild. What would be some opinions on getting possible deeper coins with this situation. Hopefully I can get back out by the end of March when the snow starts to leave.