With the Komodo Dragon, we run 6.5 to 6.9 final drive ratio with "F" brushes and purple motor springs, on tracks tighter than yours. Keep in mind that different brushes in the motor may require different gearing, but F, 767 and Hurricane Gold brushes are all in that range.
Are you rebuilding the motor, changing brushes and cutting the commutator regularly? If not, this is very important to maintain performance.
Also keep in mind that motors will vary due to manufacturing tolerances, so one KD may need a different gearing than the next (no more than 1 or 2 teeth normally).
Not sure on your stock gearing...try contacting Garrett at Team Brood, maybe on their thread, to check.