Hi, and welcome to the forums
Do you have the link to the internet article claiming the K-3 isn't all that fast? I wonder what their metrics are. I have the K-3, and every aspect of its operation is fast. As for continuous shooting, Ricoh / Pentax rates the K-3 at 8.3fps. There are some cameras with a higher burst rate, and plenty with a lower rate. Only you can decide if 8.3fps is enough, but I'd suggest it is
The combo you're looking at is fine for street photography. The camera itself is perfect for most types of photography... the 18-55 lens is a "kit lens", and there are the usual image quality limitations associated with that (the same is true of any other brand's kit lenses). I'd recommend you go for the WR version of the 18-55, as that would give you a weather-resistant combo you can use in the street without worrying about a bit of rain here and there.