AFAICS the main thrust of i7 and i9 are high frame rates for gamers, even when the CPU does not itself include a graphics processor. My own view is that if one is not doing high frame rates in HD or UHD graphics, the i7 and i9 are probably not the best value.
These days my own calculation is often what best can I get for the lower power consumption ... 35W or 65W TDP. The other thing I do is put a value on the extra performance and decide if it's good value for money. 200% more beer tokens for 25% more performance is not a great return.
FWIW, I usually compare CPUs
++ here ++How on Earth does one best compare chipsets and motherboards