[Perfectlap]

cheap air pressure gauges are garbage. I've seen differences of as much two pounds. I'd check with my longacre and then test the el cheapo I bought at pepboys during autocross events. The gauges on those portable inflators are just as bad.
Low pressures are more desireable because you know they cut out understeer. If the car has more understeer people will take turns at much slower speeds. That's what the car makers want, they don't like drivers being daring in their cars and ramming a wall or highway divider. I don't think the recommended pressures have anything to do with optimum performance.