B777-200 FLT CREW CONCERNED WITH NCT APCH CLRNC FOR RWY 28L VISUAL APCH TO SFO WHILE SLOWLY OVERTAKING A B757 ON APCH TO RWY 28R AND TWR CONCERNED WITH SUCCEEDING TFC TO RWY 28R.

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WE WERE CLRED BY NORCAL APCH FOR A VISUAL APCH TO RWY 28L AT SFO WITH TFC (B757) AHEAD LNDG ON RWY 28R. WE WERE ALSO INSTRUCTED TO MAINTAIN 180 KTS TO THE BRIDGE. AS WE APCHED THE BRIDGE; IT WAS EVIDENT THAT WE WERE GAINING ON THE RWY 28R TFC; SO I SLOWED TO FINAL APCH SPD TO REMAIN BEHIND THE PARALLEL TFC. EVEN AT OUR APCH SPD; WE WERE FASTER THAN THE RWY 28R TFC; SO THAT BY THE TIME WE REACHED THE RWY; WE WERE ABEAM THE OTHER ACFT. I REALIZE THAT ATC IS ATTEMPTING TO MAX THE TFC INTO SFO; HOWEVER; I DON'T THINK THEY SHOULD ISSUE A SPD RESTR WHEN THEY WANT YOU TO REMAIN BEHIND A LEADING ACFT ON CLOSELY SPACED VISUAL APCHS. ADDITIONALLY; THEY SHOULD ISSUE SOME INDICATION OF SPD DIFFERENTIAL (EG; YOUR SPDS ARE MATCHED; OR; YOU HAVE A 30 KT OVERTAKE ON TFC) ESPECIALLY AT NIGHT. THIS WOULD GREATLY ASSIST THE PLT IN PLANNING A SAFE APCH. ADDITIONALLY; AFTER LNDG; SFO TWR REQUESTED THAT WE EXPEDITE OFF THE RWY DUE TO LNDG TFC BEHIND US. SOMETIMES THE SFO OP CUTS THE SAFETY MARGIN A LITTLE TOO THIN.