Since a bit after they first came out. Used the E-Trac for several years before that. I like the machine and use it mostly now for beach/water hunting. Did hunt goldfields years back, but not with the CTX. I've looked for references to peoples' exploits with the CTX and nuggets and generally it appears the 6" coil is just able to get something larger than 1 oz at something under 4" soil depth. I wouldn't expect much sensitivity from the 11" coil toward buried 'pickers' or smallish nuggets at depth. Of course there are lots of factors that determine sensitivity, such as size, shape, and composition (alloy) of the nugget, so there is no absolute reference.
Like I said, go for it, you never know what you're going to find.