It's been a long time and my copy's buried deep in boxes, but I'm only familiar with the 64.3 megaton estimate from the 1.5kg antimatter/1.5kg matter stated warhead configuration on page 129.However, the TNG Technical Manual is also inconsistent with itself regarding torpedo yields. At least two other entries on page 141 gives wildly differing torpedo estimates based on the primary and secondary destruct mechanisms. Approximately 2.39 gigatons and 5 kilotons respectively. It is uncertain whether these yields would come before or after the 74% efficiency is applied.
Anyway, 'Enterprise' Canonically indicated that torpedoes have an insanely wide dialing range.