"the RTX 4090 is between 2x and 4x faster than RTX 3090 Ti,"

I would suggest you look at the fine print - the 2x to 4x (MS Flight Sim only) claims are based on using DLSS 3.0 - Poser doesn't use DLSS.  In rasterization, there is very little improvement, based on their own slides.  Nvidia pulled the same stunt moving from the 20 series of cards to the 30 series.  The actual uplift was less than 50%, not 200% - 300%.

Oh, and that "RTX 4080 12Gb model"? - you might want to look at it's actual specs - it is a completely different die, and it's performance when not using DLSS is less than an RTX 3080.  It is an RTX 4070.  Nvidia realizes that if they told their gaming base that a 70 series card is now 900USD, there would be riots at Nvidia's HQ.

If you want to spend 900USD - get an RTX 3090 - they are selling at the same price as the faux 4080, and will be much better for rendering.  The 3090 has twice the ram (24Gb), 33% more CUDA cores (which is what we care about.  3090 - 10496 CUDA cores.  Faux 4080 - 7680 CUDA cores).  The 3090 also has twice the bandwidth.

If you are getting a 4090 (FE are triple expansion cards, so you need to factor that in) don't forget to budget for both a new Power Supply (450 watt board power means you will probably want a 1000 watt PSU to deal with transients) and check your wiring in the house (USA only); you will be pulling right at what the circuit breaker can handle.  Ask me how I know.....

The good news is that if you have a 20 or 30 series card - Poser will use multiple GPUs for rendering.  I asked about this and the Poser team said that adding a 2nd card for rendering cut render times by 30% in their tests.  You can get a pair of 2060 (12Gb) for about 600USD

In the next month or so, there are going to be literally thousands of 30 series cards popping up on ebay since Etherum has finally moved to PoS.

In addition - most AIBs are sitting on literally months worth of 30 series cards.  EVGA is exiting the GPU business, but according to their CEO, they are sitting on about a year's worth of 30 series cards

I am looking to get 2 RTX 3080 (12Gb) for my next system (1 new, 1 used).