That will likely be fine. OneCNC does not require exotic hardware, but you can always make use of the fastest CPU/MB combo when it comes to intensive toolpath calculations for 3d toolpaths. I run OneCNC on hardware from 2 to 5 years old, and it runs well enough most of the time that I've no incentive to upgrade my equipment til it dies Mind you, I don't run many multi-megabyte nc programs.
Just stay away from pre-Athlon64 CPUs, if you're an AMD user, and stick with either ATI or Nvidia video so you have reasonable hope of seeing regular driver updates, in case of a video problem.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)