XRAY - Model racing cars

Hello all!
I am still confused about gearing and or gear ratio should be used on my T4-14
Next weekend I will attend a sanction race and we will be using a handout motor, which is Speed Passion MMM 13.5T
The race is open boost and timing (non blinky)

On last race, which is no sanction race, I used Orca RX2 13.5T motor with Orca VX esc
I ran 84 spur and 27 pinion which give me around 5.9 FDR if my calculation is correct and along with moderately esc setup
The temperatures on both esc and motor was ok and below limit
The car is easy to drive with very smooth bottom end

After reading some posts, I found out that some people suggested to run around 7.5 FDR. Even on Setup Station apps Alex also using around that 7.5 FDR which is way up the FDR I used on my last race with RX2 Orca
Now my questions are:
1. What are really the basic knowledge on determining a gear ratio we should use or start with for T4-14?
2. Should esc and motor temperatures use as a guide?
3. If the basic FDR is somewhere around 7.5 than why the 5.9 I used, which I think wayyyy off, got around 80 degree after 5 minutes race?

Please note, the track is high grip medium sized asphalt. Ambient temperature is around 35 degree
And my next sanction race will be at the same track
All the expert please give me some knowledge about this gear ratio things so that I could decide which number to start with for different size and conditions of tracks that I might race in the future

Thank you all and have a great day

Do you have any pictures or video of your track?

At our track the guys running ORCA 13.5 boosted are geared around 6.5;

Here is another picture of the track from different agle

https://www.dropbox.com/s/z0uhtf6hfkimt ... 2.png?dl=0

I would start around 6.5 and check motor temps

Guess work based on other tracks. Once you've done a few you can normally guess roughly what gearing to use.
If you are not sure, keep an eye on motor temps after 3-4mins and see how it goes.

Skiddins