SIMULTANEOUS VISUAL APCHS WITH SPD CTL AT SFO; CA; ON RWYS 28L&R.

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DURING A VISUAL APCH TO RWY 28R SFO; WE WERE TOLD TO MAINTAIN VISUAL SEPARATION FROM ACR ON OUR L. I ASKED IF HE WOULD LAND PRIOR TO US; AS I COULD NOT TELL; AND THE CTLR SAID WE WOULD PROBABLY FLY SIDE-BY-SIDE. HE THEN TOLD ACR TO MAINTAIN VISUAL CONTACT WITH MY FLT. IT BECAME APPARENT THAT ACR WOULD STAY IN FRONT OF US; SO HOW WERE THEY ABLE TO MAINTAIN VISUAL CONTACT WITH US. BOTH FLTS WERE GIVEN SPD ASSIGNMENTS WHICH FURTHER COMPLICATES THE QUESTION OF WHAT TO DO IF YOU BEGIN TO OVERTAKE THE OTHER FLT -- NAMELY; HOW CAN YOU AVOID AN OVERTAKE AND ALSO MAINTAIN AN ASSIGNED SPD? THIS SEEMS LIKE POOR PROC BY THE ATC CTLR. ALSO; IT IS COMMON TO HAVE ACFT COME FROM BEHIND AND PASS MY ACFT ON VISUAL APCHS TO RWY 28R&L AT SFO. THIS SEEMS UNSAFE AND IT IS VERY; VERY DISTRACTING WITH TCASII ALERTS AND VISUAL DISTR AS WELL. ADDITIONALLY; HOW CAN AN ACFT PASS MY ACFT AND CONTINUE TO MAINTAIN VISUAL CONTACT WITH MY ACFT AFTER HE IS FAR AHEAD OF ME? I SUGGEST ALL ACFT BE PROHIBITED FROM PASSING ANOTHER ACFT WHILE ON A VISUAL APCH.