Hi Robin, I'll throw in some of my observations. I'm not there yet, so take my words with caution.
Robin Woods:
… I'm just asking - based on your experiences as I don't have any data source or understanding psychiatrist to turn to - whether you think I should just go for this now and not fear 3rd path DN too much? I'm not sure I could even stop if I tried at this point as noting in daily life has started to become habitual.....
One thing I've been realising over and over again during the last months is: I'm not doing this anymore, this is doing me now. (I know, sounds like an awful platitude …) Unlike during the first two paths, especially the first one, it seems to me like I essentially have lost control over the process. Maybe I could slow it down by avoiding practice completely, but my impression is that actually stopping it isn't possible. I haven't tried that, though.
Robin Woods:
… Are the benefits I'm likely to gain in terms of sensory clarity and awareness likely to outweigh DN effects at this stage? I don't seem to be able to depressively 'ruminate' at the moment for instance...
Or is it true what they say about 3rd path being very confusing and kinda like a macro/fractal Dark Night itself? …
To me the way to third path is significantly different than from getting to the first two. It is much more gradual. You are going to complete the progress of insight again and again. It takes me usually 3-6 weeks after which I run into a week or so full of fruitions. Often it seems like nothing has changed. But after a while you see that some solidity has been chipped away. It's like your view of the world is slowly corroding, is getting more and more porous. Accordingly, the dukkha ñanas show up much more often, but they also tend to pass much faster, and they haven't yet been nearly as intense as during first path (second path dukkha ñanas were kind of a cake-walk for me). Strangely enough, one of the more unpleasant things I run into from time to time is doubt. Doubt in the sense of: is this leading anywhere?
I like fivebells suggestion of branching out into different practice tools. That's what I've been doing too. On the way to first path I spent more than 95% of my formal practice time doing noting. My second path practice was almost completely open awareness without noting (suggested by my teacher). Now I'm doing metta, open awareness (mostly without noting), some kind of surrendering practice (a bit like centering prayer), and I spent a few weeks doing some koan-like thing. I had to be pushed a little bit by my teacher to try these things out, but I'm happy he did. At first I feared that I would loose momentum. But after a while I had to acknowledge that I was cycling, no matter what kind of practice I was doing.
One last suggestion: Try to work with a teacher, it's really helpful!
Good luck!