Talking to someone who has read some of the books, I was told that Godric was basically a footnote in one of the books, but that some other guy was Eric's real sire. Either way, I'm talking in the altered universe the show has created it was explicitly stated that none were higher than Godric in the New World. It was later stated or implied (can't remember which) that Eric was now the oldest/highest. However, if Russel is 3k+ years old on the show or even was a vampire before Eric, then one or both of those statements is untrue.