This is absolutely false and I read you other comments on the subject as well. I am not sure whether it is deliberate, but what you are saying is absolute nonsense made to sound credible by inserting a random technical term like "pipeline" here or there. It is sad that the quality of posters on Slashdot has decreased to the point where laughable misinformation is moderated as "informative".
64 bit code might get slower because pointers occupy more memory. Frequently that is offset by more registers and smart encoding. End of story. What you are saying is wrong.