EATX isn't quite an official standard. Different manufacturers have slightly different ideas about their "standard" EATX dimensions. An EATX board is basically longer in one dimension, it sticks "down" a little further when mounted (sideways) in a standard tower/chassis configuration, mostly to provide enough extra onboard space for one or two extra PCIe/PCI card slot(s). A tower/chassis which isn't tall enough won't have enough (internal) room for the mobo and the PSU together.

"3D" could mean lots of things and I'm unfamiliar with Photogram. So I can't say whether they'll leverage GPU or CPU better. An 18C/36T i9 CPU will cost as much as a lesser CPU plus a pair of 1080Ti GPU cards. If your 3D work is heavily GPU-based, or runs a lot of CUDAs and PhysX and FP32 then more GPU will be smarter than more CPU. To be honest, I think 18C/36T is almost unuseable unless running a ton of simultaneous VMs ... but then again, that's what I used to think about once-mighty 8C/16T and it didn't take very long to learn that I want/need even more.

128GB of DDR4 will populate 8 (already doubled up) DIMM slots at maximum capacity, a heavy load on the CPU iMCs. And it'll be hard to maintain stable (DDR4/XMP) overclock on an iMC which services so many cores and caches. I'm not sure what the exact specs are, but the i9 won't natively support non-JEDEC DDR4-3000, it'll more likely be JEDEC DDR4-2400 or -2667. The advantage of X299 HEDT is quad-channel memory bandwidth, which multiplies still further at higher memory frequencies ... if your work is heavily RAM intensive then you might actually need to tradeoff more CPU cores vs faster (overclocked) DDR4, the simpler CPU parts will tend to run memories at higher frequencies than the complex CPU parts can, plus the simpler CPU parts tend to have faster clocks.

Rampage and Strix (and other ROG-branded mobos) provide a whole lot of features ... added cost, added complexity, reduced stability, diminished system performances (unless overclocking and stuff, lol). I'm not bashing ROG mobos at all - my "workstation" is built off one - but I am saying they're not the best choice for everyone and there's no sense paying more for a ton of bling and features if you have no intention of using them - an ASUS PRIME or -WS mobo is a more compelling and reliable choice for many professionals. A Xeon-based platform is also a more compelling price, not as exciting (though you might be surprised by what's being offered) but much more thoroughly documented and supported and reliable and *capable* at doing real hard computing work than consumer-based platforms ... and at comparable prices to X299/i9.