Guys here is a little tech p0rn for you (maybe) - I am upgrading from my i5-4570 that I got in 2014 to... Xeon E3-1231 v3 which is equivalent to i7-4770 - it has 8 threads instead of 4 and is overall around 30% faster. Here is full comparision:

http://cpuboss.com/cpus/Intel-Xeon-E3-1231-v3-vs-Intel-Core-i5-4570

I have been eying Haswell i7s for a while but their price is too high for me to bite, around 100 euro is not worth it IMO, but today I searched on Ebay and the Xeon E3-1231 was under 50 euro from Germany and I even got 5% off from Ebay hehe

I think I can sell my i5 locally for around the same price, so it could be a nice free upgrade for me.

Why not go with something more modern like a Core i3-10100F or even Core i5-10400F and sell your old system? old intel motherbaords usaully sell for high prices.

Congrats on the upgrade. Sounds like a good deal. I upgraded my old PC that I gave to a friend, when I bought my new one last year, from an i5 4690k to a Broadwell i7 5775c overclocked to 4.1 Ghz. In gaming due to the eDram L4 cache reducing memory bottlenecks of DDR3, it slightly outperforms the i7 4790k @4.7 GHZ. They go for $120-$150 on eBay though, which makes them cost ineffective. I was lucky to find one for $90. 

Make sure you are looking at your DDR3 timings/clock-rate. That is often what causes the CPU bottleneck with these Haswell/Broadwell chips. With a decent motherboard for overclocking and good ram that can run at higher voltages you might be able to get up to 2100 Mhz or even 2400 Mhz with 10 timings. 

Meh, I don't see the point, my PC is super responsive as it is. Sure I can't play modern games with 200 fps, instead I get 100, so what? My monitor is 75 hertz anyway.

My Xeon will destroy all your ryzens and 10th gen heaters ( ͡° ͜ʖ ͡°)