Can tell you almost for certain that seeing how the GB Pro is a dedicated gold detector, while the XT-705 is known as an all-purpose detector, that the GB's 11" coil will definitely hit on deeper gold than the 705's 10.5" DD HF coil will. Actually it is said that other than on larger nuggets the 10.5" DD HF coil is not particularly good on gold and especially on the smaller gold like its two smaller companion coils will hit on. Do know that the XT-705 in its prospecting mode with a 6" DD HF 18.5 Khz. coil will hit on gold down to 1/40 th of a gram which is pretty good for an all-purpose detector. If by chance you are talking about depth on coins, then I think the ML 10.5" DD HF coil would hold its own against the GB Pro's 11" coil and more so in trashy environments.