If you want 100fps in all of today's games at 4K ultra settings, nothing exists that will do that yet. The 4090 gets close but there are a handful of games like BL3, CP2077, Dying Light 2, Warhammer III which even a 4090 cannot achieve 100fps averages in.
The NVIDIA GeForce RTX 4090 Founders Edition offers huge gains over its predecessors. It's the first graphics card to get you 4K 60 FPS with ray tracing enabled, and upscaling disabled. Do you prefer 120 FPS instead of 60? Just turn on DLSS 3.
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You were right that now is a bad time to buy a new GPU - we're right in the middle of a generational transition. The midrange cards that usually shift the price/performance curve for the whole market aren't out yet, and the halo cards are shockingly expensive still, coming with early-adopter tax.
If I were in your situation I'd pick up a used 3070 on ebay as a stopgap and reassess the new GPU situation in 6-12 months. You're unlikely to lose much money on a 3070; If you buy one now for under $400 you should be able to get the majority of your money back by selling it on again in 6+ months.