I haven't found coins any deeper than the E-Trac (9" max so far) but I have found more coins at 9" in 40 hours with the CTX than I had with the E-Trac in 100 hours (same spot). I attribute that to better signal processing, better separation, faster recovery, etc.
Regarding finding more coins in hunted out spots - yes and no. If the spot doesn't have as much iron, as much iron mineralization, trash, etc. then I am only seeing a few more targets (maybe 5% - 10%) and I have to work hard for them. If the spot has more iron then I am seeing a huge performance gain from the CTX. I estimate that in one small strip (around 10ft X 40ft) I have found more coins at 8" and 9" with the CTX than I did with the E-Trac. The important thing there is that I hunted that strip from many angles, with 3 different coils (6X8SEF, stock and 13" Detech), etc. I ran both machines at manual 30 there though I have been running the CTX in auto more than I did the E-Trac as it runs slightly hotter.
I agree with Jason - I got the CTX because the E-Trac was too much for my back. An expensive upgrade but I finally found a machine in the E-Trac that worked in my somewhat iron mineralized ground and wanted continues success.
So, to justify the cost - Do you waterhunt? The CTX is an awfully expensive machine if you don't. The overall improvement is not huge but as I said, imo it depends on the spot. I know you can't really quantify a machine with %'s but overall I'm guessing the CTX is like a 15% - 20% enhancement in performance, but it costs like 100% more. So, you got to weigh the benefits and of course see how much money you have to spare! The E-Trac with the 13" Detech is a very nice machine and I think it reduces the distance between the machines a bit more.
Albert