Um, I am not sure if the reason for the PJ is as stated here.
When I was racing my rs125, it had the pj carb and a BPS unit. The power jet would switch off past peak power- this has the effect of extending over rev as otherwise the jetting goes too rich past peak power. This was easily verified on the dyno.
I need to post my dyno runs off my recently completed 300. With air box, peak was 61hp. With air box removed, peak was 66hp, with more power from around 8500 up. The air box is definitely staying off!!! Power drops off quite dramatically past peak. I have an opinion that this is perhaps a design brief of the tyga pipes? The reverse cone looks quite aggressive -perhaps to reduce a tendency to over rev? The same dyno has runs from well tuned production racing mc21s putting out 45, so it shouldn't be too far off..
300 is a hell of a lot more impressive than the 250 was on the road