Yeah, its a bit more a gaming thing and some specific functions, etc.
Having said that, DDR5 does have a couple other advantages, like somewhat easier to get higher memory sticks, so doing say 64 GB with just two stick of DDR5 is likely to have more options then DDR4.
Also, DDR5 has some basic ECC built in, so that’s nice.
But in general, pushing polys around isn’t a RAM intensive thing, at least not where speed matters.
Personally, mostly just not a fan, but having said that, I’ve never used a large/wide screen that’s curved or otherwise. So go with what you like. Frankly for content work, pixel density, colour accuracy and a reasonable refresh rate matter more.
Much like what Joseph said and I’ve already pointed out. You need to be very clear on your use case as to if two 4090’s are worth it.
If you don’t GPU render using Cycles (or some other GPU renderer) then its pointless. A second GPU will make no difference to viewport performance, modelling, sculpting, texturing, etc, etc. For all of that the second GPU sits there and does nothing.
Even if you do use Cycles, if what you render doesn’t fit in 24GB VRAM, then any 4090 is ‘useless’, as you got no choice but to render via CPU.
However, if you do use Cycles and can render in 24GB VRAM and do a lot of rendering, either stills or especially animation, then a second GPU could be well worth it.
Another area is video editing, some apps/filters/effects can and will make use of the GPU to speed things up and depending on the software they can use more then 1. So a heavy video editor may in fact have a 2 GPU system.
So yeah, just need to be very clear on what you do or plan/expect to do in the next 6 months and make sure the gear will actually be of any use for it.
Don’t try to ‘future proof’, if you’re getting a second GPU now, because you think it may be useful in a couple years time, that’s pointless. By then a 5090 or 5090 Ti will be out, it may well be twice as fast as a single 4090 and cost less (both to buy and run) then two 4090’s now.