What exactly does "responsiveness" refer to in terms of keyboards? I mean, there's tactile feedback, but I don't think you mean that. Is there some other quality of keypresses that I'm not aware of? Like some keyboards being able to convince the computer to do things that no other keyboard can make them?
I 'd hazard the guess that "responsiveness" in regard to keyboards is probably another overhyped-by-superstitious-gamers property that nobody can find any objective testing criteria for other than the usual anecdotal evidence like "I just bought me a $200 'board and I can tell you, man, that thing is clearly so much more responsive than my old $20 board" - which is a result of two other properties: a) the better mechanical quality of the keys (taking less force and time to press down that switch) and b) the placebo-effect that comes with any expensive purchase.
Latency also shouldn't be too much of a problem actually - after all, keyboard electrics are pretty straight-forward; you hit a switch and a rather simple microchip turns it into some codes that get sent on the PS/2 bus, or a bit more complicated chip generates an USB event. It's not like a TFT monitor's electronics where an entire picture gets manipulated or buffered before being displayed.
It's pretty safe to assume that the latency on keyboards is pretty damn small (like single digit milliseconds at most, I'd say) and mostly determined by what's going on with the keypress-signals inside your computer, not the keyboard itself.
I've yet to see any good tests for latency of keyboards, since it's pretty hard to precisely trigger an mechanical event without any point of reference to the exact time in the computer where the event is recorded. So all you will find about different latencies of keyboards is anecdotal evidence by gullible gamers.
Bottom-Line: Buy a high-quality board with switches that feel good for you and are easy to be tapped quickly (Cherry blacks or perhaps reds if you can find them). The physical mechanics of the switch are probably the biggest factor that determines the quickness of any given board.
Chris