Have you tried renting a cloud instance to determine if getting better hardware would fix the issue? There you can try 512gb of ram to determine if that is the solution before investing in purchasing the hardware only to determine that the limitation was elsewhere.
Several people here have made a benchmark of their workload, and made it available to download. Then people with different systems will download and run the benchmark and post their times. Would that be an option so that you can find an optimal solution before spending money?
Can’t be done unfortunately. Quadspinner stopped selling their GOAT software Gaea 1 from sale so people can only get the demo version which is super locked down, no tiled builds, and maxes out at 1024x1024. People would have to pirate if they didn’t have it already. Gaea 2 is available, but despite being out for a year it’s far too buggy (corrupt projects, crashes, memory leaks, etc) to be used for any serious work in my experience.
And yeah the limitation is RAM, the memory required scales up by power of 4 for each increase in resolution at least. What will be interesting is when I buy the threadripper system and seeing how more memory channels on the same CPU architecture might affect build times even with the same core counts.