I'm choosing a GPU for a mostly 1440p gaming build with a 9850X3D. Local prices are about $850 for a 9070 XT, $1,100 for a 5070 Ti and $1,450 for a 5080. I also have a 1000W power supply.
Is the 5080 worth the extra money if I want to keep the card for six years or more, or would one of the cheaper options make more sense?
I'd start with the 9070 XT at those prices. For conventional rendering at 1440p, it's close enough to the 5070 Ti that the extra $250 is hard to justify unless you specifically want Nvidia's features.
Put the $600 difference from the 5080 aside for a future upgrade. A card that's good value now plus an upgrade later may be a better use of the money than paying a big premium to avoid upgrading.
The 5070 Ti is the middle ground if ray tracing and DLSS matter to you. It costs more than the 9070 XT, but gets you Nvidia's feature set without the full jump to the 5080.
Check benchmarks for the games you actually play, with ray tracing and upscaling settings you would use. The price gap is big enough that the choice shouldn't come down to a few frames per second in games where both cards already perform well.
The 5080 is the pick if you want the most performance of these three and can comfortably afford it. It makes more sense if you expect to move to 4K or want demanding ray tracing settings, not just because the CPU can handle it.
That said, nobody can guarantee six years at the settings and frame rates you want. You can keep using a GPU for a long time, but future games may require compromises.
I'd treat long-term software support as a consideration, not a promise. Nvidia's upscaling and other features are appealing, but availability of newer features can differ between GPU generations. Check which features each specific card supports rather than assuming either brand will get every future update.
The CPU is strong enough that you don't need to pick a GPU just to match it. Decide what performance and settings you want at 1440p, then spend accordingly. The 1000W supply gives you room for the 5080, but it doesn't make the extra cost worthwhile by itself.
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Tervin.6q:
Even at 1440p, wanting high frame rates with ray tracing could make the extra headroom useful. Whether it's worth $350 over the 5070 Ti is a separate question.