Lets make it clean.
Clock speed is one thing, actual compute performance is an other. Also price/performance and performance/consumption comes into play.
The fastest AMD (fx-8350) is about in par with the i5-3570, even though it has more (yet smaller) cores and a higher frequency. It consumpts more power and costs nearly the same. AMD mobos are cheaper though.
Also, intel does not pruduce 3 core CPUs. The i3 has only 2 cores, the i5 and i7 have 4.
Currently, the AMD video cards are better price/performance-wise than the NVidia 6xx series, so i would highly recommend to choose one of those (Hd-7xxx series)
Unless you have unlimited money and resources, i would forget both about the SLI and Crossfire - a single high end card can run basically anything on 3 monitors.