GY6 What more upgrades are worth it?

[Snailspace]

I got a 125cc (short case) GY6 that I upgraded to 175cc, replaced the whole head.
it orginally came with 13 or 14g rollers. I had to go all the way up to 17g sliders to achieve top speed and be able to cruise at a reasonable rpm. Also installed a NCY GEAR SET (15 37). Torque is really good so i consider putting in a even longer gear set, suggestions? It does 90 km/h roughly, but i also live at 2000 meters elevation.

I see NCY sells a green Performance clutch, what does this do and is it worth it in my scenario and does it exist a reinforcement / bracelet for shortcase gy6 engines since i like to ride without the CVT cover for the looks of it with some mods.

I been looking at getting a stainless steal exhaust since the original is starting to rust. I am getting different answers everywhere. Will the performance increase any with a free flowing exhaust and jetting it up? Will I lose a lot of lowend acceleration?
Is a cone filter nescerry to get any performance gains from it? I like to keep the Original Airbox since cone filters are useless in the extreme rain here during the rainseason.

I got the Blue racing CDI. I see the racing cdi being sold together with Electrode Sparkplugs and coil. Will this do anything or is this a pure scam?

Lastly any upgrades I have not mentioned here that you guys recommend? Thanks