Standard 65-66 Starfire gearing was 3.23. 3.42 was the next hottest factory gearing, but I expect you could have gotten deeper if you knew how to check the boxes.
2.73, 2.93 and 3.08 were the other factory gear ratios.
Sounds like you might have had 3.73 or so under there. My 64 with 3.42 has no trouble passing the century mark and then some, but the 66 I had 30 years ago with 3.23 would also not get much past 100.
