Try a 36 rear sproket- you'll probably love it.
Unless you are very heavy or riding a lot of very steep long hills, it'll be faster and won't bog down with a normal China girl carbureted fairly normally.
I have a 50cc bike with a 39 alloy sprock- made from an GT front chainwheel
and a 66cc with an alloy 34 - evolved from the original 44 to a steel 36 and eventually to the 34- in flat Florida, it pulls me along quite well 30 mph -plus cruise, 35 plus top speed with normal kit speed carbs
The one thing you'll notice right off is that you get to a nice speed without the motor racing wide open and so there's a lot less vibration- it just feels like you are more in control- you could still open it up screaming, but may not want, or need to.
light narrow alloy wheels help too. It's usually not that hard to add a 700 C skinny wheel to the front like a chopper motorcycle, but you'll probably have to change the caliper brake. Once I tried that, I had to have one on the back too, and now all I have on both bikes. But you have to more carefully ride within limits- I raced road cycling for a long time so I'm comfortable with the fast wheels.
good luck
The photos are of the evolution of the same bike my 66 cc Micargi-
with original beach tires back in '09 (far right), with a front 27" wheel (indoors)about 2011, and with the baskets on last summer and painted silver