Fishnut, don't think of it as jumping ship; think of it as adding a rowboat to your ship!
Or more like a speedboat! I use the etrac as my main machine, but the nox is a great addition to the arsenal because of its speed. I've picked stuff out of heavy iron areas that the etrac couldn't find. The lighter weight is a big difference too. The only problem, and its a big one in my belief, is that the tones are no where near what they are on the etrac; it's not even close. That said, you can do a fair bit of adjusting to the pitch, the tone of the pitch, the volume that each target range registers at and other settings.
Its different, and it will take a bit to learn how to set it up the best way for your liking (I'm still learning what to tweak), but its going to serve you well. If you've been hunting along time, you have a long list of sites that were productive in the past. You'll be able to go back to those sites and pull more good targets from there; the Nox is that fast and that different in how it seeks targets that you will pull stuff the etrac has missed.
Be sure to get the 800, not the 600 as you don't have the ability to adjust the settings the way the 800 does. The 800 has more variability for the recovery speed and gives you more precise refinements, plus you have the even higher recovery speeds of 7 and 8 on the 800. And since the lowest setting of 1 on the 800 can not be matched exactly by the 600, you can theoretically get a bit more depth out of the 800.
A lot of people dismiss the individual gold modes as useless on the 800 saying "I dont look for nuggets". Their theory is, if I don't hunt for the item that mode is specifically geared for, its of no use to me. The software for each mode is different in how it interprets the signals coming back to the machine, so target signal processing is different in gold mode than it is in park mode. Even using gold mode in an individual frequency will still find (non gold) targets that the other modes may have missed, and its partially because of that software interpretation difference in each mode. It would be like going over an area with a Garrett Ace 250 (6.5 khz) and clearing it of all signals. And then going back over the same area with a Garrrett AT gold (18 khz). And you would find new targets with the AT Gold because its a different frequency, AND because its interpreting things differently. In a nutshell, each mode on the Nox is like its own individual machine, so having the gold modes can be of use. The gold modes are great for relic hunting too.
I just found out last night that the 600 does not have the ability to save a separate user mode that you can access quickly in order to cross check a target, kind of akin to the Quickmask on the E-trac. That can be useful at times, like setting that extra user mode to a 10 khz single frequency setting so you can cross check for potential rust like bottle caps etc.
The Nox has various advantages over the E=trac (weight, recovery speed, possibly processing software/interpretation), but it falls short in the tonal response range and target ID range. Like Happa54 said, if they could combine those differences, it would be a beyond killer machine!