I am very happy with my 3rd gen Intel Core i3. It runs at 3.4Ghz with two cores and 4 threads. It has never held me back from anything I have tried to do. When I built it I thought I could eventually swap in a i5 or i7 with same socket down the road, if needed. But have never needed to! It has been running great for over two years!
I would probably have more performance headroom with an i5 or i7, but I never hit 100% CPU with what I have. I mostly work with softsynth VSTi's and can load and run as many as my RAM will hold.
The truth is most i3's are sold with budget systems, so everybody assumes that they are crippled. But that is mostly due to the quality of the overall components used in off-the-shelf computers. If you build your own and select quality parts, this little beauty can be a real sleeper! Plenty of bang for the buck!!!
I have 8GB DDR3-1600 RAM and run Windows, Sonar, and all VSTs from an SSD.