DDR4 Memory question

Does PC4-21300 2666 MHz memory with a timing of 15-17-17-35 run at the same speed as against PC4-17000 2133 MHz memory with a timing of 12-14-14-27?

It's not running at the same speed as it has higher frequency. Hard to say what will be better just because of many other factors and one maybe most important - cache clock, which is limiting max bandwidth.
2400 CL12 will probably have better access time but lower max bandwidth so all depends what are you doing. However I doubt you will notice any difference in daily work.

Right now one of the best options is Kingston Predator 2666 14-14-14 or 3000 15-16-16 as price isn't much higher than 2400/2666 kits of other manufacturers and performance will be higher.