you can also install viper/srx style reeds, not sure what you have to do to make them fit, ive done it on a sx with a little grinding. they are wider, and have larger pedals for more area to flow through. your twin for some reason has the same size reeds as a tripple, you would think they would need a larger reed area as they are flowing more air through them than a tripple. if you do a search you can find the aritcle with pictures to show the difference between them.
as for the notch, i dont see how it can do anything for that motor, the port is not blocked, as for a bog down low i would check your float level, clean carbs, check with dealer to see if jetting update was done to the sled as there was one for the twins.