If you look closely the gear separation between the CG10 and CG13 in terms of ratios is not much different, the overall ratios being shorter make the difference feel less but it's very close if you compare figures.
I find the biggest difference between 1st and 2nd gear the main issue. Plot the overall drive ratios in excel and see for yourself, there's not a huge difference between boxes, especially 1st, 2nd & 3rd. If you want to see a radical difference try plotting them against the ratios of the 31V short ratio box from the March R and then you'll see what a more perfect gearbox would be for a well tuned K11, (except for the fact that, like a 1.0, it will be a bit of a buzz bomb on the motorways).
All ratio information is available to see on the K11 gearbox wiki. March R boxes are like rocking horse poo though......