There does not seem to be any definitve answer to this question, but if you have one, I would like to hear it :grin:
I have seen the very fast C ataglyphis piliscapus, but he Sahara Desert ant (cataglyphis bicolor) should be abel to run up to 1 meter pr. secound according to this (http://www.pnas.org/content/92/7/2994.full.pdf see note 22). That must be near the record.