Hmm... the Overclockers increase the EU usage by alot. I think they multiply it by 4, while doubling the speed.
So if you use 4 Overclockers the machine uses up 256 times more EU, which means that it very often has to be supplied more than 512 EU/t And if you cant supply it enough EU/t it simply wont do anything.
If you aim at supplying every machine with 128 EU/t (Medium Voltage) 2 Overclockers will increase the amount of EU used by the factor of 16. Since most machines use around 5 EU/t this will bring them up to 80 EU/t which should be supplyable.