Oh boy, I could run away with this question, but I'll keep it tame.
I would still go with the 79cc. If I have a bigger bike that can fit it, then I'd go 212 simply because of the available upgrades, and way more power than the 79cc. However, the 79cc is a decent, reliable crate that can do pretty good for power if you have your own cnc machine. You can make your own parts. 3d scanner + cnc means one can scan a part, beef it up or make it lighter in a CAD, and then form that part out of raw aluminum. Also, a cnc machine means high precision, high reliability head milling. A solid, flat surface every time, precisely milled to exactly the dimensions set in the CAD program.
Then again, I could go two stroke again, but build it from scratch. I would start with a high quality case, and then build the motor with handpicked parts, starting with the crankshaft, jug, conrod, piston, and clutch. Also, while building this engine, all internal parts that are not the clutch will be soaked in two stroke oil prior to assembly. This way, I can ensure proper lubrication during assembly and any excess won't cause much harm at all. The clutch will be separately lubricated. I'll do as I suggested a few times already: take a syringe with a small tube, grab some heavy grease, and very carefully apply a dollop of grease to each bearing in the clutch before spinning it to distribute that grease. They never lubricate these clutches and it pisses me off. Bearings anywhere need to be properly lubricated so they don't damage themselves under load.
