Need advice for cylinder kit choose (50->70)

Hi all! First of all - sorry for my english)
I`m owner of scoot with good oldie engine Hiper 1 (aircooled). Already installed tuning parts are Pollini Hi-speed vario, LV Touring (yep, i know, it`s similar to stock pipe, but i love how it looks and how it sounds, and i don`t want to install more powerful exhaust), and Redsponge in stock box. Carburetor (Dellorto phva 17.5 ; also already got the set of replacment main jets), reed valve and rear clutch are fully stock.
Everything works fine, but it`s time to get more power\speed. So, i`m talking about "basic tuning" 70cc cylinder kit, which will have good resource, wide RPM band if it`s possible (not for track or something like that, of course; just day to day city riding or long time trips) and maximum compatibility with my already installed parts, especially with exhaust pipe. Which to choose? Pollini sport? Dr. Evo? Maybe Alu with 2 rings, like Airsal? Or simply classics - MS Sport?

 

Athena aluminium sports kit or look at pmtuning site for their aluminium x-tech kits for that engine