Monitor cpu usages with Msi Afterburner. If nearing or at 100% in the games you play then an i7 8700 would help with that. 9700 would be alright too but would prefer having Hyperthreading especially on the primary core to be beneficial for command que latency. 9900 would be going overboard tbh and cooling requirements more major than usual. Would still need decent cooling for an i7 processor though, just not as much for the i9.
Imho, 8700/8700k would be a significant step up with 6c 12t in more cpu intestine games. If you do get fairly high cpu usage, an 8700 will help a lot.