I just dont see how it can make a difference in performance. Unless it is a weight issue, and balance.
Well, you do wish to ride fast don't you!?
and a swing arm mounted plate will make a noticeable difference in perfomance?
1) my baggy pants will have more of an affect on performance.
2) any loose buckle or belt on my riding jacket will have an affect on performance.
3) my non aerodynamic riding boots will have an affect on perfomance
4) my stock front turn signals that stick out will have an affect on performance
5) my side-stand will have an affect on performance ( by the way..that weoghs more than a side mounted license plate )
I can continue naming things that "can" affect performance while riding but you see where im going with all this.
I just dont see how a tiny piece of metal sticking out can have such a drastic affect on your bikes handling. If it does I had better take off my "Dice" valve stem caps because thats going to throw my wheels out of balance [smirk]
Unless you are European.... in that case arent your plates like 4x the size of ours? That would explain why you can feel the difference in having it side mounted or rear mount. On the side I could see how that would act like a boat sail