It creates less separation generally.
My testing at default+ Speed Threshold seemed to indicate as well there was something off with the timing of AI Screen plays, at least with the couple of teams I have tested this with. Reducing the threshold even to just 40-45 seemed to give a chance to the AI to make the read/play on these HB screens. (At 0, in practice mode, certain screen plays that previously were resulting in sacks over 50% of the time became unstoppable against the same defenses). The CPU still takes sacks on screen plays with a threshold reduction, but fewer of them.
Putting speed threshold below seemed to reduce the sacks on PA plays slightly, but the results were definitely within the "margin of error" and are inconclusive. So far, the best way to reduce sacks on PA passes seems to be a slight increase in Pass Blocking (55-60) combined with a significant decrease in Pass coverage (0-25). Testing with selected pass/defense combos (PA Post vs Cover 3/5 man blitz) reduced the rates of sacks from ~6.5/10 to ~3.5/10 (note, with WRC at 45 and QB Acc at 40, the completion rate with Pass coverage at <25 was still below 50% on this particular PA play & defense).