They didn't have too many personal names in general, IIRC about 20 or so commonly used, including numeric ones (there's even Decimus - I guess they had big families). And looking at how Ceasar is always Julius Ceasar (while his personal name was Gaius) it looks like they didn't use it too much outside of family and close friends. Which kinda makes sense - if you know 10 guys with personal name Gaius, it's not very useful to say just "we're having a party at Gaius' place tonight".