I agree with leenoox. I have tested a spread of CPUs on 13x rigs; the CPU makes a significant difference in stability; please don't use celerons with 13x rigs.
My Celeron's are on 8x rigs and they cause too much instability. I would not recommend them at all. Invest little bit more in better CPU like i3 (I haven't used Pentium CPU's on mining rigs but I guess those are not much better than Celerons), it will save lots of frustration and downtime and it will pay itself off. A lot of times my Celeron rigs were frozen for 6-8 hours while I was at work -> lost revenue. I don't feel like babysitting them 24/7 and they will be replaced soon
