The RX 7900 XT still has latency issues in VR yes, even after the July driver update with improved VR performance. Probably something to do with the chiplet architecture needing some refinement. This is the first chiplet-based GPU.
The RTX 4070 is architecturally closer to AMD’s RX 6000 series than to the RTX 3000 series though: it has low memory bandwidth and uses an enlarged cache instead. This leads to high power efficiency and performance does not suffer much in most applications.
But I expect that similarly to the RX 6000 series’ Infinity Cache, it will cause reduced performance in high-res VR flight simulators, at least compared to cards like the RTX 3080 (Ti) and 3090.
Also, the RTX 4000 cards are overpriced.
For now, I’d recommend to look for a good deal on a last-gen card: RTX 3080, 3080 Ti, or 3090.
RX 6900 XT or RX 6950 XT can be had really cheaply sometimes too, so may be worth it.
But no, with current drivers and prices I don’t recommend buying either of the cards you mention. Unless you absolutely need stuff like AV1 encoding perhaps…