I just got a full yoshimura exhaust for my grom. I was looking for performance gains more than sound but couldn't find much on that so I will give you my opinion.
I feel the pipe gained more torque and mid range, not a ton but noticeable. It's takes off better and you don't have to give it a ton of gas to get it going from a stop. The top end to me seems to be the same as far as speed goes.
As far as the sound, it sounds like a 250 four stroke dirt bike. Pretty loud! Maybe I'm old but riding it in town is what I use mine for and sounds awesome. My wife uses hers to commute to work and she nor I would use the yoshimura for wide open stretches on a daily basis unless you plan on wearing earplugs. I already had a bad experience in the selection exhaust for dodge challenger rt
I have many years of motorcycle experience so hope you don't think I'm blowing smoke.
1991 ct70 stock
1991 ct70 bored
2013 ktm 300xc
2014 grom black
2014 grom red