Hello man :
That and ROPUs (render output units). Also take into consideration PCI E generation and the technologies the GPU has. For instance Free Sync has higher latency than G Sync. Saying a GPU is faster because of it's clock speed is almost like saying a GPU is better because it consumes more power.
Are you crazy ? Everyone knows that performance is proportional to how much money you spend !
Wait .... how come 4 Titans is slower than 3 ?
Lol *buys four Titan X, attempts to SLI, fails miserably and blows PSU in the process*