You can only put so much shit in a 6.5 LB bag. What do you plan to do with it? maxed out motors require a lot of maintenance, and can get very expensive. Turbos are a waste of money. Realistically your only going to get 8,200- 8,500 RPM out of a GX200 before it starts to lose power and start to eating itself. And if you start calling local kart shops, you will get only one answer, write me a check and I will build you whatever you want. I know it sucks but it is what it is. If you know how to talk, try out of state shops. They will not tell you secrets but they will make you parts and give suggestions, if you know what you want. Your not going to get a good steak at a seafood restaurant.
Good luck, homie.