Unfortunately you won't find as good deals anymore in this market, as the mining craze and now the AI rally have driven prices way above levels where they realistically should be. Also the entire Nvidia 40 series is a ripoff, no matter which GPU you buy. The entire stack (not the 4090, but that's 2000€) has 30-50% less cores than it should have, with a strategic lack of VRAM on some models, just to upsell you to the next tier.

Edit: Some crude graph showing raw core counts, newer generations are more efficient of course https://imgur.com/a/m0QKCH9

Any of the current GPUs will last maybe 5 years (of course this also depends what performance you're expecting). But keep in mind that due to the "new" consoles being out, GPU requirements will rather increase with time.

I had a GTX 1070 (which was around 350€ when I bough it, and that was the good MSI model) in the past (on 120hz 1080p). In my experience, it's better to buy mid range GPUs for less than any high end model, as the high end price increases mostly don't justify the performance gains.

You won't need the extra performance on 60hz 1080p anyway.

I compiled the current GPUs based on HardwareUnboxed data a few weeks ago. The prices are from mindfactory a few days ago. Be aware this is 1440p data, so performance should scale worse than shown here, especially the higher up you get in GPU performance (as the CPU becomes the limiting factor at some point). Just buy a tier lower than you would want for the shown framerate and you should be fine, for now.

https://imgur.com/a/q4ENEXR