Benchmarks suggest there’s little meaningful between the two, would it be worth doing to access the 4th gen architecture and the frame generation capabilities?
Today I run MSFS at 1440 with most settings at ultra and achieve framerates in the mid twenties (heavy congested areas) to mid fifties.
I have a 4K monitor I’m not currently using (have it on my work pc) as I found the frame rates taking more of a hit with this.
Are you actually CPU limited? That’s my guess.
CPU limited, for sure, that’s a feature 
With that limitation though does a 4th gen card make any real difference?
The other (and quite reasonable) choice is to wait and see what MSFS 2024 brings to the party.
The frame generation is awesome. Absolutely love it.
That said, I got my 4090 before I got my 13900K, and much of the total frame rate increase came when I upgraded my CPU from the 10900K too.
The 3070Ti will double your frame rate and that part’s awesome. But when you’re dropping into the 20’s, you’re getting low enough that it can affect feel/handling. You’ll get 40-50 fps with doubling, but the responsiveness to input will still be at 20 times a second. The 3070Ti will improve your experience and won’t be a waste of money, but you’ll want to budget for a CPU upgrade when you can as well, to really get glassy smooth performance with the 4000-series card.
I get the impression that FS2024 is going to have better multithreading, so might be less CPU-limited, which would make the 4070Ti upgrade add even more. But that’s a “maybe.”
I had the 3080Ti and I woulnd´t change it unless you go to a 4090, which is around a 40% faster and has double VRAM capacity. You have a superb card from the old series, capable of high fps even on 4K and with 384 bit memory, and you will change it by one with same 12GB but 192 bit memory and less shaders computing capacity instead. Such low memory amount may be a problem in MSFS at dense areas with high screen resolution and detailed textures for instance, as game will hit 10GB easily under DX12 in most cases under 4K.
The 4070 core clocks are faster, yes, but that low memory bandwitdh combined with only 12GB capacity is a no go in my opinion as it results in 3080Ti having double texture fill capacity even while working at lower clocks than the 4070 for instance. But even the 4080 still has just a 256 bit one so 3080Ti is still faster there. Anyway the 4080 may be a better choice in case you have budget restrictions to go to a 4090 or you can´t find it with a significant sale discount as I understand it´s expensive. That one has noticeably faster clocks that 3080Ti and 16 GB instead, which makes the upgrade more reasonable. But it´s still a 256 bit card (same as the 2080 was years ago). That was a terrible error from NVIDIA in my opinion as it should have been a 384 bit one as the 4090 in my opinion to be a really attractive alternative instead of the 4090. For that and other reasons I decided to go directly to the 4090.
Frame generation is nice but it produces many noticeable artifacts when panning camera around, even on the 4090. Be aware of that because it´s not magic, even if it´s needed due to the low fps in game while in ground for instance.
Cheers
FWIW I have a 12GB 4070Ti on my TV PC and (with a 13700K CPU) it maintains smooth frame rates from 60-120 fps on my 4K TV. The texture memory difference vs a 3080Ti doesn’t really affect the overall performance due to the other improvements.
Note that “noticeable” is subjective. 
I use DLSS all the time when flying and don’t notice any artifacting that’s coming from frame generation. I’m sure people sensitive to it can pick out artifacts, but it’s nothing I notice when flying the planes.
I don´t mean the 4070Ti is a bad card, only that taking it when he comes from a 3080Ti is not what I would do because both cards can perform quite similarly in many aspects, even if they are from different generations. Most likely he would just see a small difference only in raw fps and the main difference would be the availability of frame generation. But for optimal results with frame generation you want to have high raw fps anyway. I would just take the 4080 or 4090 if possible. Anyway 4080 is not what 3080 was, compared to the 3090. In the 4080 case there´s a significant downgrade compared with the top line 4090, not just less VRAM.
The 3080Ti can also maintain >60 fps on 4K and ultra settings in MSFS, even with 125% scaling and TAA (and that´s raw, as it has no frame generation). I have used it since MSFS was released with 1080p and later on with 4K and it didn´t suffer when I switched to 4K. In terms of memory is therefore a really fast card and basically has the same specs from the 3090 but with half the VRAM, so it´s almost top line from the last generation. It has been one of my best GPUs in the past years, just to be honest.
However in MSFS it starts to suffer on ground or at dense areas with such settings because its VRAM is almost fully used quite frequently, which leads to severe fps drops in MSFS until data swap has been completed. Its slower core clock also leads to some lag while panning camera on such dense areas. That was the first thing I noticed when I moved to the 4000 series as the camera panning improvement was relevant, even without frame generation. But game still puts performance to its knees on crowded international airports, so I didn´t have (nor I expected it) more than 50fps on ground with the 4090 on dense airports, while I could have 40 fps with the 3080Ti. We all know that´s a limitation of current game engine so we would need to wait and see if FS2024 really solves that or not.
Cheers