Mach4 will run very good on most PCs and Laptops but you really need to have an external motion controller. Like the Ethernet Smooth Stepper, UC300ETH, Ether-Mach or PoKeys.
The performance of the processor itself has to do more with the types of operations you are running, number of axis, resolution, macros, etc… Usually, as far as the processor, an I3 should be plenty fast.
We always recommend using a Solid-State Drive (SSD), especially using macros, as they are called from the disk. Using a dedicated video card will also improve performance.