What CPU to get?

Just recently upgraded my gpu (550 xt to 6750 xt) pretty big jump, now I notice some bottlenecking so I think it’s time I upgrade my cpu. I was looking at the i9-9900k but I honestly have no clue about what’s the one to get.

I would like it to let me play the newer, more demanding games and ofc gta 6 if it ever decides to come out.

Any help would be greatly appreciated

Parts:

CPU: i5-9600k

MBB: z390 ud v2

RAM: corsair vengeance rgb pro ddr4 2x8gb 3200mhz

PSU: corsair rm750x

GPU: 6750 xt