By replacing 03PSD with 04PSD for BS oplev, I compared their performance.

The measured oplev spectrums are shown in the attached figure 1 (RED 04PSD, BROWN 03PSD), while the electronic noise comparison with ADC noise is shown in the attached figure 2 (RED is elec noise, BLUE is ADC noise, GREEN/BROWN are integrated noise).

We could conclude that both 03PSD and 04PSD have almost the same performance. The difference in position resolution is not affecting their performance now. So I guess this position resolution maybe related with beam size.