Jason,
fortunately I’ve laid hands on a handful of really nice six string basses.
I was nervous to commit to a 6 string at one point. I even had a build in que and cancelled it perhaps 2017ish.m(not smart) I was exploring options then and wanted to try something less expensive at the time. I ended up with a Roscoe Skb for example that had a massive neck, similar to the Yamaha JP2 that I had. Oddly, both of these where still very comfortable necks in comparison to the direction I wanted to go and did end up going.
It really does come down to adjusting technique to the bass.
The Z3 6 is hands down the fastest neck I’ve played and it is my favourite.
In Contrast the Forte is probably the heftiest neck I’ve played and own. It’s massive but again, I still love it and find it a pleasure to play. 10 yrs ago I wouldn’t have said that and I don’t think I would have been able to keep it but I think as my overall technique has improved I’ve learned how to exploit the strengths and of a bass and perhaps even minimize the weaknesses with set up or other adjustments.
I think this is a really important factor when making the transition to 6.
Even my first Z3 6 (the maple one) was an adjustment from a 5 that seemed a bit daunting but working at it with reason (chording,tapping,soloing) pays off.
I know you’ve gone thru a few basses over the last couple years and some of which are certainly

worthy and I really gotta say with this. Explore what you have!!!!
Adjust the set up,
change the strings,
explore pick up heights with headphones on,
try different strap lengths.
All of these factors offer up different pros and cons to sound and comfort. Force yourself to try some things that seem a bit counter intuitive like action. Raise the action a tad if your a member of the “lowest action possible” gang. Don’t marry yourself to a certain brand of string. Base that on what plays best with the bass in-particular for your desires.
I know you probably know all this but just to reiterate it’s importance, It will make any bass you have that much more enjoyable. (Including that gorgeous AB2)
I don’t think this is really the info you were seeking from me but perhaps it’s a precursor to me trying to answer your question a little better or not.
Scale length comes into play when comparing. Currently I can compare the Zs 37” B, forte 35”, bongo 34”.
As mentioned the Z neck is by far the speediest neck to play and the design of the bass makes the 37” no further of a reach then the 35” forte. I do play a lot down low and this does factor in to how much I can struggle with a song. I find there to be more total hand movement or perhaps shoulder/elbow movement when moving around on the Dingwall. The scale is longer. Makes sense. For some of the fastest stuff I have to do I honestly have had to work a bit harder at my technique with left arm movements vs being more stationed on a shorter scale instrument like the bongo. Sound/clarity being the obvious trade off/perk of the dingwall.
Up high… chording can be a challenge on fanned frets. Depends what you need to do. I think a lot of this can be corrected with alternate hand/finger positioning but honestly I don’t do much chording, I’m more in the tapping camp and the dingwall neck is awesome for this.
When it comes to the sound way up the necks of the various scale lengths there 100% is differences created by the length of the string BUT… there is ALOT of variance in the sound you get based on more factors then the length of the string.
My opinion the tension and sound on the shorter C is an asset of the dingwalls. The thing is, you also need to be conscious about how you play. You really really should play with the fan. What I mean is as you move from the Low B to the high C you should move your hand position in the same direction as the fan keeping the same distance away from the bridge as you move to the C. Play with it on the G on your 5 and you will see(hear). The tone does actually change quite dramatically as you move your plucking hand closer to the neck. Hope that wording makes sense.
Other factors:
-Strings
-action (including pick up height)
-AND mass and woods(IMO). There is a thick richness on the forte that is not as present on the dingwall and I strongly believe this is due to the massive maple neck. That and the neck thru factor making it a completely different build then a bolt on dingwall.
the snappy brightness of a bolt on dingwall is a totally different flavour then a heavy neck thru instrument. Depending on the music you play one may be better suited. I’m not in a camp that favours one vs the other. It’s purely personal taste for me and I like both.
you won’t find a Shortness of Harmonic content on the dingwalls IMO. They are still plenty plucky enough when strung with proper strings for that to be a non issue. Again, strings matter.
I’ve tried a few KIESEL/Carvins and they are great basses but honestly there is a quality “feel” that comes with some others with larger price tags. If you buy the right bass at the right price, even if Unsatisfied you won’t lose substantial monies. You previously haven’t shied away from high dollar basses and I’d recommend not letting a price tag deter you if considering a six, especially if you are really willing to commit to it.
The combustions are a great option. They do compare to most other basses found in the price range. That said, they are nothing like a Z3 6 and any assumption from one to the other should not be made.
I do think 18mm is a really nice sweet spot but adapt to 17ish well on a 6. I wouldn’t want any tighter.
A Skjold 6 (parallel fret) or a LeFay(Fanned fret)is very high up my gas list which may spec very well for your interests.
Don’t let your hand size be your determining factor either. I remember seeing this little monster before I got into 6ers.
TL;DR: blah, blah, blahblah internet opinion
Hopefully something useful