I think the reason for the lack of "opinions" is that maybe people aren't sure where to begin. There are potentially a LOT of variables involved with your question, and not a lot of information (i.e. target images) on which to base any guesses. For starters, eric32 is correct - the Berger twist rate calculator recommends a minimum 11.5-twist barrel for that bullet using a velocity of 2650 fps, elevation of 500 ft, and a temperature of 65 degrees. At higher velocity, temperature, and/or elevation, stability would be better, but may still not provide a sufficient Sg to obtain the full intrinsic BC of that bullet. A 168 gr bullet such as Berger's 168 Hybrid, or a slightly shorter 175 bullet such as Berger's 175 OTM Tactical bullet would be better choices.
Next - you stated in your post that you "got no discernable node". What exactly does that mean? It might be helpful if you had some target images of the groups you shot. One possibility may be that you didn't notice much of a change in group size across the charge weight window of Varget you tested. However, it is not always the case that you will see groups shrink noticeably within an optimal charge weight window. What you really want to be looking for in an OCW test is two or three successive charge weight increments where the centerpoints of the groups don't change on the target (i.e. - same POI). IMO - 0.4 gr increments are a little too large for the best results with a .308 Win case. I would suggest using 0.3 gr, or even 0.2 gr increments. Once you have identified a stable charge weight in the middle of a window where POI changes on the target are minimal, then you tighten up the groups using seating depth.
It is possible that you might benefit from doing some preliminary seating depth optimization, if that will make the subsequent charge weight testing and analysis clearer. If you can't find any helpful information online or from Nosler about where their bullet might like to be seated, just do the test yourself. Using a charge weight closer to the lower end of your test range, I would try something like -.005", -.010", -.015", -.020". -.025", and .-030" (i.e. off the lands) using 3-shot groups, just as a preliminary seating depth optimization. I'd be surprised if you didn't find something in that window that looked better than the others. If necessary, you could try Berger's coarse seating approach for VLD bullets, which covers a much wider range
https://bergerbullets.com/getting-the-best-precision-and-accuracy-from-vld-bullets-in-your-rifle/. Bear in mind that this is simply a very wide window (i.e. - very coarse) seating depth test. I personally would only try it if I couldn't find some seating depth that looked halfway decent in the much narrower range I listed above.
The problem with going to these lengths is that if your precision is suffering primarily because you are under-spinning the 175 RDFs in a 12-twist barrel, none of these approaches will necessarily help improve the results you're getting. So I would keep in mind that using a shorter 168 or 175 gr bullet that doesn't require more than a 12-twist may be your best bet. The two Berger options I listed above are both relatively forgiving to load and have very good BCs for their weight class.
