Re: Gear range or Cassette size for shifter kit
It's not the number of gears on a cassette that will help you go faster, rather it is the number of teeth on the gears that help with speed. The fewer teeth on the cogs on the cassette the better for speed.
Other than that I'd wait on Pablo or Ghost0 to chime in with their recommendations.
"I would rather be exposed to the inconveniences attending too much liberty than to those attending too small a degree of it." - Thomas Jefferson