It sounds like you did a really good job. I can’t believe how well a Grom can handle with good suspension and tires.
I’m in love with those Kenda KD1 Kwick tires. I will definitely be buying another set. They are confidence inspiring. I don’t really care how long they last. The safety and cornering performance you gain from the additional traction is worth it in my opinion.
My buddy just ordered a high compression piston like yours for his bone stock Grom. We will install it this winter sometime. He also ordered an exhaust and intake too. He will be running the TB cam and DHM reflash. I can’t wait to ride it and see how much of a difference the piston makes.
We previously installed a 14 tooth sprocket as the first mod. It made a big difference. My bike is still blowing his away though. When that Yoshimura ST-2M cam gets into the upper revs, it really walks away. He is tired of getting dropped, so he is ordering parts. It’s a deep rabbit hole from here.
You are right about re-gearing the Grom. Feels like the bike should have come with that gearing from the factory. At least for the North American market anyway.