Hello, the quoted “stock” spur gear would be for a 78T one, as that is basically the std spur on a Lazer ( I believe since the first ZX5 they have not changed ), the 76T is primarily used for stock motors like 10.5T, 13.5T etc.
What staggers me is that you say the ZX6 is too punchy with a Speed Passion 8.5T motor and 25T pinion against a 78T spur, when I ran my ZX6 indoors at York earlier this year I was running a LRP X20 8.5T and 20T pinion against 78T spur, I did not find the car to be punchy - slipper was tight also.
I did find that it was far too slow , so I had to turn up the settings on the LRP Flow to make the car run at an acceptable speed. I know for a fact that that motor was very quick in another car I had used it in.
The Lazer’s gear ratio’s mean that you need to run quite a fast motor in it , more so than what you would run in say a B-Max4. I have now got a 6.5T X20 , same gear ratio as before = Perfecto !!
Hope this helps you - Maybe ??
Cheers - Rob.