the carb thing has a lot to do with induction also, a reedvalve is more efficient than a piston port and therefore can be satisfied with a smaller carb... hence all the blaster polini's out there. it is as much about dynamic airflow as it is about steady-state airflow, if not more. a big carb has increased eddies, and can have negative effects on the dynamic airflow. its not going to slow you down, its just not necessary. if anyone on here can honestly say they have gone from a properly tuned 19phbg to a 21phbg and seen an increase, i'd be very surprised. what most people can probably say is that they were too lazy to play with their needle, pilot jets or emulsion tubes and their bike ran better with the stock guts in the 21 phbg than the 19 phbg.
SHA carbs have the emulsion tubes set up for 4 horsepower bikes at most, so when you start running a pipe and your jetting needs to be really fat in the upper midrange and top end, and really lean in the bottom end, the one-size-fits-all jetting will give you a lean condition in the bottom, which makes them boggy. its 95% about tuneability.
and yes.. no more jetting questions on the PT forum. if you cant jet your shit, stick to stock until you learn it.