a lot of you(especially those who have already invested in the high-end stuff) will have a second say on this post... but, in reality:
whether u get a $250.00 "signature" chip or a $35.00 cheap copy of a signature chip off eBay or other source, the outcome-performance wise will ALWAYS be the same.
In essence, what a performance chip does is it re-maps the power curve of your car; and among the parameters altered is the rev limiter. in a performance chip it is programmed to cut-off at a higher RPM than a stock chip.
Then of course, in order to achieve the higher horsepower ratings, the ignition timing is also re-mapped(altered)/advanced.
Fuel flow, not necessarily(except through the fuel pump relay as commanded to switch ON or OFF by the DME). Fuel flow(rate and pressure) is managed by your fuel pump and ur fuel pressure regulator. Performance buffs change the fuel pressure regulator to hold a higher pressure at the injection rails-that allows for more fuel to enter through the injectors per millisecond opening time.