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
G4560 has 2 cores and 4 threads, much better than other Pentium and celerons.
I have a 13x rig running on a g4560 without issue. I think the g4560 is the lowest CPU that can be used effectively with a 13x rig. A g4560 is essentially the same CPU as the g4600 with 100 MHz lower clock speed; they are about $7 different in price. I suspect that the g4600s are A binned g4560s ( the exact same CPU with less defects (all Chips have defects) and the + 100 MHz).