Hi,
I’ve had a GC6 Tournament Edition with Simonis 860 for about 1 yr now. I wrestled with the BW/Diamond/Rasson question like many do. In the end the desire to have a part of the Americana I grew up with in my home and a personal preference for the looks/feel of the GC drove my decision. It looks and plays great, and I’m quite happy with it. Construction & feature wise I believe it to be on par or better than GC4’s. I’ve never seen a GC5, but IMO each generation of GC made subtle improvements.
There are minor issues with fit & finish of the pocket/casting hardware, but these are truly minor. However, can be a bit psychologically annoying in context of a $10k ish premium product when compared to a new Diamond. This
thread & this
thread both have quite useful & detailed feedback that I think would be worth your time.
Since I started playing pool again after decades away, I have now played on a lot of different GC and Diamonds and become much more educated on table issues. As many people will tell you, if you want a BW to really be top notch then you really need to have a good/experienced table tech set it up for you. I think Diamonds design is simply better in this regard - it appears that Diamond's rail/frame design are setup to tighter tolerances at the factory and final assembly of the table is more "plug&play", doesn't require as much care and precision by the installer, which results in a product that requires less complexity to deliver and setup and final assembled fit/finish/specs are more consistent. BW appears to have more variance in their pocket sizes/angles and literally have more moving parts. Practical examples; when you order a Diamond Pro Cut - regardless of who sets it up - for the most part you will get 4.5" pockets and 141° pocket facing angles which makes for a very nice crisp pro level table that is plenty tough and perfectly within WPA specs, but order a GC6/TE and you might end up with pockets anywhere from 4.25-4.5" and 141-143° PFAs. These variances can really affect play - mine ended up with pockets in a range of 4.25-4.35" & 143-144° and it plays super, super tough, tougher than several other CG/Diamonds with much smaller mouths in the 4.0-4.25" zone. Especially on a new table with fresh rail rubber and fast cloth - its super touchy, essentially if the OB touches a rail or hits a facing with too much speed it's just not going in. I wanted a really crisp table, but it's really much more frustrating than I had intended and quite miserable for casual players.
A good analogy for the BW/Diamond thing may be comparing a 1911 pistol to a Walther or CZ. If you're shooting USPSA type stuff and want a 1911 to run really smooth and accurate, you'll need an expert to hand tune it (Les Baer, Wilson, etc) - whereas pretty much any Walther, CZ, or even Glock will just work great out of the box. I'm not a car guy, but I guess it might be also like comparing a vintage muscle car to a modern japanese sports car.
Anyway I think you'll be happy with any new GC6, but since you want the "GC to end all tables", I think you should try to nail down what you really want in terms of pocket specs (very personal decision, no "right" answer, there are other AZB threads on that, we all have our own opinions and use cases for home tables) and get in touch with a knowledgeable table tech to get their inputs and a relationship established first, before ordering the table. If you don't have one local, consider working with one of the well known ones to travel to you; it's only money
Hope this helps and good luck on your journey.