I've pulled over people because they were swerving and their BAC was 0.06.
One drink (glass of wine, pint of beer, shot of liquor) does not take you to 0.05. You have to take into consideration the person's weight and how fast they were drinking.
If you drink a glass of beer, you are going to reach 0.01. If you chug a glass of beer in 20 seconds on an empty stomach, you will reach 0.01 faster, not higher, than if you had a dinner and it drank the beer over a course of 30 minutes.
In police academy, we spent one day where half the glass drank and half the class practiced giving the SFSTs. One beer after an hour took people to 0.009 to 0.011. So, it would take about 5 beers to get to 0.05.
What they are going to have to do is change the SFSTs if they lower the BAC to 0.05. It is much easier to pass the SFST, walking a line, standing with one foot up, at 0.05 than at 0.08.