NCT Controller described a conflict event on the SFO final when traffic assigned a Visual Approach to Runway 28R over flew sighted traffic inbound for Runway 28L; citing pressure to establish side-by's as a causal factor.

Narrative

Air Carrier X was down the bay when he checked in [and] I descended him to 4;000 FT. Air Carrier Y was cleared 'Tip Toe Visual Approach Runway 28L.' My intentions were to make them a pair. I had a NUQ point out to the visual approach. I wanted to turn Air Carrier X base in a timely manner to avoid conflict with the Arrival. I called traffic and turned Air Carrier X base. He called traffic in sight [and] I advised to maintain visual separation with which he complied. I called traffic to Air Carrier Y and he reported traffic in sight; but did not respond to maintain visual separation. I then cleared Air Carrier X for the Visual Approach. Air Carrier X went over the top of Air Carrier Y and climbed and proceeded to go around. I informed the Supervisor that I was unsure if the go around was because of TCAS or too high for the approach. I'm not sure that I have any recommendations for procedures or changes. I do however think that we are constantly scrutinized for not making the 'side-bys' as accurately as possible and that affects pushing the aircraft limitations to the utmost levels.