You mean what RPM/MPH? That all depends on what you're doing. If you're commuting, you want to shift as low as possible for MPGs. If you're racing, you want to shift as high as possible for max power.
How fast do you shift? As fast as possible. Time between gears = loss of efficiency/mpg/speed.
How fast do you shift? As fast as possible. Time between gears = loss of efficiency/mpg/speed.
